Support for treating vascular bifurcations

ABSTRACT

A prosthesis is disclosed for placement across an ostium opening from a main body lumen to a branch body lumen. The prosthesis comprises a radially expansible support, at least two axially elongate longitudinal members, at least one of which can be fronds, extending from an end of the support, and a circumferential member connected to at least one axially elongate longitudinal member and unconnected to at least one other axially elongate longitudinal member.

BACKGROUND OF THE INVENTION Field of the Invention

Embodiments of the present invention relate generally to medical devicesand methods. More particularly, embodiments of the present inventionrelate to the structure and deployment of a prosthesis having a stent orother support structure and at least one, and in some implementations atleast two fronds for deployment at a branching point in the vasculatureor elsewhere.

Maintaining the patency of body lumens is of interest in the treatmentof a variety of diseases. Of particular interest to the presentinvention are the transluminal approaches to the treatment of bodylumens. More particularly, the percutaneous treatment of atheroscleroticdisease involving the coronary and peripheral arterial systems.Currently, percutaneous coronary interventions (PCI) often involve acombination of balloon dilation of a coronary stenosis (i.e. a narrowingor blockage of the artery) followed by the placement of an endovascularprosthesis commonly referred to as a stent.

A major limitation of PCI/stent procedures is restenosis, i.e., there-narrowing of a blockage after successful intervention typicallyoccurring in the initial three to six months post treatment. The recentintroduction of drug eluting stents (DES) has dramatically reduced theincidence of restenosis in coronary vascular applications and offerspromise in peripheral stents, venous grafts, arterial and prostheticgrafts, as well as A-V fistulae. In addition to vascular applications,stents are being employed in treatment of other body lumens includingthe gastrointestinal systems (esophagus, large and small intestines,biliary system and pancreatic ducts) and the genital-urinary system(ureter, urethra, fallopian tubes, vas deferens).

Treatment of lesions in and around branch points generally referred toas bifurcated vessels, is a developing area for stent applications,particularly, since at least about 5%-10% of all coronary lesionsinvolve bifurcations. However, while quite successful in treatingarterial blockages and other conditions, current stent designs arechallenged when used at a bifurcation in the blood vessel or other bodylumen. Presently, many different strategies are employed to treatbifurcation lesions with currently available stents all of which havemajor limitations.

One common approach is to place a conventional stent in the main orlarger body lumen over the origin of the side branch. After removal ofthe stent delivery balloon, a second wire is introduced through a cellin the wall of the deployed stent and into the side branch. A balloon isthen introduced into the side branch and inflated to enlarge theside-cell of the main vessel stent. This approach can work well when theside branch is relatively free of disease, although it is associatedwith increased rates of abrupt closure due to plaque shift anddissection as well as increased rates of late restenosis.

Another commonly employed strategy is the ‘kissing balloon’ technique inwhich separate balloons are positioned in the main and side branchvessels and simultaneously inflated to deliver separate stentssimultaneously. This technique is thought to prevent plaque shift.

Other two-stent approaches including Culotte, T-Stent and Crush Stenttechniques have been employed as well. When employing a T-Stentapproach, the operator deploys a stent in the side branch followed byplacement of a main vessel stent. This approach is limited by anatomicvariation (angle between main and side branch) and inaccuracy in stentpositioning, which together can cause inadequate stent coverage of theside branch origin commonly referred to as the ostium or Os. Morerecently, the Crush approach has been introduced in which theside-vessel stent is deployed across the Os with portions in both themain and side branch vessels. The main vessel stent is then deliveredacross the origin of the side branch and deployed, which results incrushing a portion of the side branch stent between the main vesselstent and the wall of the main vessel. Following main-vessel stentdeployment, it is difficult and frequently not possible to re-enter theside branch after crush stenting. Unproven long-term results coupledwith concern regarding the inability to re-enter the side branch,malapposition of the stents against the arterial wall and the impact ofthree layers of stent (which may be drug eluting) opposed against themain vessel wall has limited the adoption of this approach.

These limitations have led to the development of stents specificallydesigned to treat bifurcated lesions. One approach employs a stentdesign with a side opening for the branch vessel which is mounted on aspecialized balloon delivery system. The specialized balloon deliverysystem accommodates wires for both the main and side branch vessels. Thesystem is tracked over both wires which provides a means to axially andradially align the stent/stent delivery system. The specialized mainvessel stent is then deployed and the stent delivery system removedwhile maintaining wire position in both the main and side branchvessels. The side branch is then addressed using the kissing balloontechnique or by delivering an additional stent to the side branch.Though this approach has many theoretical advantages, it is limited bydifficulties in tracking the delivery system over two wires (See, e.g.,U.S. Pat. Nos. 6,325,826 and 6,210,429 to Vardi et al.).

Notwithstanding the foregoing efforts, there remains a need for improveddevices as well as systems and methods for delivering devices, to treatbody lumens at or near the location of an Os between a main body lumenand a side branch lumen, typically in the vasculature, and moreparticularly in the arterial vasculature. It would be further desirableif such systems and methods could achieve both sufficient radial supportas well as adequate surface area coverage in the region of the Os andthat the prostheses in the side branches be well-anchored at or near theOs.

Description of the Related Art

Stent structures intended for treating bifurcated lesions are describedin U.S. Pat. Nos. 6,599,316; 6,596,020; 6,325,826; and 6,210,429. Otherstents and prostheses of interest are described in the following U.S.Pat. Nos. 4,994,071; 5,102,417; 5,342,387; 5,507,769; 5,575,817;5,607,444; 5,609,627; 5,613,980; 5,669,924; 5,669,932; 5,720,735;5,741,325; 5,749,825; 5,755,734; 5,755,735; 5,824,052; 5,827,320;5,855,598; 5,860,998; 5,868,777; 5,893,887; 5,897,588; 5,906,640;5,906,641; 5,967,971; 6,017,363; 6,033,434; 6,033,435; 6,048,361;6,051,020; 6,056,775; 6,090,133; 6,096,073; 6,099,497; 6,099,560;6,129,738; 6,165,195; 6,221,080; 6,221,098; 6,254,593; 6,258,116;6,264,682; 6,346,089; 6,361,544; 6,383,213; 6,387,120; 6,409,750;6,428,567; 6,436,104; 6,436,134; 6,440,165; 6,482,211; 6,508,836;6,579,312; and 6,582,394.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a prosthesis constructed inaccordance with the principles of the present invention.

FIG. 1A is a detailed view of the fronds of the prosthesis of FIG. 1,shown with the fronds deployed in broken line.

FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. 1.

FIGS. 2A-2E are lateral views showing embodiments of a stent havingfronds in a rolled out configuration. FIG. 2A shows an embodiment havingserpentine-shaped fronds, FIG. 2B shows an embodiment having filamentshaped fronds, while FIG. 2C shows an embodiment having filament shapedfronds with alternating shortened fronds. FIGS. 2D and 2E illustrate anested transition zone configuration with two different stent wallpatterns.

FIG. 2F is a lateral view as in FIG. 2D, with the added feature of acircumferential link to assist in maintaining the spatial orientation ofthe fronds.

FIG. 2G is a lateral view as in FIG. 2F, having a helical frond.

FIG. 2H is a lateral view as in FIG. 2F, with the fronds modified toenhance crossing of a secondary stent while maintaining robustscaffolding in the ostium.

FIG. 2I is a lateral view as in FIG. 2H, with a modified stent sectionhaving enhanced longitudinal flexibility.

FIGS. 2J-2K are lateral views as in FIG. 2H, with a modified stentsections having open cell constructions.

FIG. 2L shows an embodiment with a tapered transition zone and aproximal serpentine section of relatively low stiffness.

FIG. 2M shows a lateral view of another embodiment of a stent havingfronds in a rolled out configuration, wherein reservoirs are providedfor holding a drug to be eluted into the vasculature.

FIG. 2N shows another embodiment of a wall pattern for a prosthesisadapted for deployment at a bifurcation.

FIG. 2O shows an expanded configuration of the wall pattern of theprosthesis of FIG. 2N.

FIG. 2P shows another embodiment of a wall pattern of a prosthesisadapted for deployment at a bifurcation.

FIG. 2Q is an embodiment of a balloon expandable implementation of aprosthesis adapted for deployment at a bifurcation.

FIG. 2R is an embodiment of a self-expanding implementation of aprosthesis adapted for deployment at a bifurcation.

FIG. 2S is an expanded embodiment of a prosthesis adapted for deploymentat a bifurcation.

FIGS. 3A and 3B are lateral and cross sectional views illustrating anembodiment of a stent having fronds and an underlying deployment balloonhaving a fold configuration such that the balloon folds protrude throughthe spaces between the fronds.

FIGS. 4A and 4B are lateral and cross sectional views illustrating theembodiment of FIGS. 3A and 3B with the balloon folded over to capturethe fronds.

FIGS. 5A-5C are lateral views illustrating the deployment of stentfronds using an underlying deployment balloon and a retaining cuffpositioned over the proximal portion of the balloon. FIG. 5A showspre-deployment, the balloon un-inflated; FIG. 5B shows deployment, withthe balloon inflated; and FIG. 5C post-deployment, the balloon nowdeflated.

FIGS. 6A-6B are lateral views illustrating the change in shape of thecuff during deployment of a stent with fronds. FIG. 6A shows the balloonin an unexpanded state; and FIG. 6B shows the balloon in an expandedstate, with the cuff expanded radially and shrunken axially.

FIGS. 6C-6D are lateral views illustrating an embodiment of a cuffconfigured to evert upon balloon inflation to release the fronds.

FIGS. 7A-7B are lateral views illustrating an embodiment of a tether forrestraining the stent fronds.

FIGS. 8A-8B are lateral views illustrating an embodiment of a proximallyretractable sleeve for restraining the stent fronds.

FIGS. 9A-9B, 10A-10B and 11A-11B illustrate deployment of a stent at anOs between a main blood vessel and a side branch blood vessel inaccordance with the principles of the methods of the present invention.

FIGS. 12A-12H are lateral and cross section views illustratingdeployment of a stent having filament fronds an Os between a main bloodvessel and a side branch blood vessel in accordance with the principlesof the methods of the present invention.

FIGS. 13A-13C illustrate side wall patterns for three main vessel stentsuseful in combination with the prosthesis of the present invention.

FIG. 13D is an image of a deployed main vessel stent having a side wallopening in alignment with a branch vessel.

FIGS. 14A-14E are a sequence of schematic illustrations showing thedeployment of a vascular bifurcation prosthesis with linked fronds.

FIGS. 14B-1 and 14B-2 illustrate embodiments showing a transitionportion having a plurality of second ends opening up in differentdirections.

FIG. 15 is a schematic profile of a stepped balloon in accordance withone aspect of the present invention.

FIG. 16 is a balloon compliance curve for one embodiment of the steppedballoon in accordance with the present invention.

FIG. 17 is a schematic representation of a stepped balloon positionedwithin a vascular bifurcation.

FIG. 18 is a schematic representation as in FIG. 17, with a differentconfiguration of stepped balloon in accordance with the presentinvention.

FIG. 19 is a first step in a deployment sequence using a stepped balloonand prosthesis in accordance with the present invention.

FIG. 20 is a second step in the deployment process disclosed inconnection with FIG. 19, in which the prosthesis is positioned acrossthe Os.

FIG. 21 is a third step in a deployment sequence, in which a prosthesishas been expanded utilizing a stepped balloon in accordance with thepresent invention.

FIG. 22 is a fourth step in a deployment sequence, in which the steppedballoon has been removed following deployment of the prosthesis acrossthe Os.

FIG. 23 is a side elevational schematic view of a distal portion of acatheter in accordance with the present invention.

FIG. 23A is a cross sectional view taken along the lines 23A-23A in FIG.23.

FIG. 23B is a cross sectional view taken along the lines 23B-23B in FIG.23.

FIG. 24 is a side elevational view as in FIG. 23, with a modifiedcatheter in accordance with the present invention.

FIG. 24A is a cross sectional view taken along the line 24A-24A of FIG.24.

FIG. 24B is a cross sectional view taken along the line 24B-24B in FIG.24.

FIG. 25 is a schematic view of a two guidewire catheter in accordancewith the present invention, in position at a vascular bifurcation.

FIG. 26 is a schematic representation as in FIG. 25, showing the secondguidewire advanced distally through the fronds.

FIG. 27 is a schematic view as in FIG. 25, with a modified two guidewirecatheter in accordance with the present invention.

FIG. 28 is a plan view of a variation a prosthesis having a frondsection similar to that of FIG. 2H mounted on a deployment device, theprosthesis being shown in an expanded configuration.

FIG. 29 is a lateral view of the prosthesis of FIGS. 2N-2O mounted on adeployment device in an unexpanded configuration.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Embodiments of the present invention provide improved prostheses anddelivery systems for their placement within a body lumen, particularlywithin a bifurcated body lumen and more particularly at an Os openingfrom a main body lumen to a branch body lumen. The prostheses anddelivery systems will be principally useful in the vasculature, mosttypically the arterial vasculature, including the coronary, carotid andperipheral vasculature; vascular grafts including arterial, venous, andprosthetic grafts such as a bifurcated abdominal aortic aneurysm graft,and A-V fistulae. In addition to vascular applications, embodiments ofthe present invention can also be configured to be used in the treatmentof other body lumens including those in the gastrointestinal systems(e.g., esophagus, large and small intestines, biliary system andpancreatic ducts) and the genital-urinary system (e.g., ureter, urethra,fallopian tubes, vas deferens), and the like.

The prosthesis in accordance with the present invention generallycomprises three basic components: a stent or other support, at least onefrond extending from the support, and a transition zone between thesupport and the frond. These components may be integrally formed such asby molding, or by laser or other cutting from tubular stock, or may beseparately formed and secured together.

The term “fronds” as used herein will refer to any of a variety ofstructures including anchors, filaments, petals or other independentlymultiaxially deflectable elements extending from the stent or othersupport structure, to engage an adjacent main vessel stent or otherassociated structure. These fronds can expandably conform to and atleast partially circumscribe the wall of the main body vessel toselectively and stably position the prosthesis within the side branchlumen and/or optimize wall coverage in the vicinity of the ostium.Further description of exemplary frond structures and prostheses isfound in co-pending application Ser. No. 10/807,643, the full disclosureof which has previously been incorporated herein by reference. Variousembodiments of the present invention provide means for capturing orotherwise radially constraining the fronds during advancement of theprosthesis through the vasculature (or other body lumen) to a targetsite and then releasing the fronds at the desired deployment site.

The prostheses of the present invention are particularly advantageoussince they permit substantially complete coverage of the wall of thebranch body lumen up to and including the lumen ostium or Os.Additionally, the prostheses have integrated fronds which expandablyconform to and at least partially circumscribe the wall of the main bodyvessel to selectively and stably link the prosthesis to the main vesselstent. The fronds may be fully expanded to open the luminal passagethrough the main branch lumen. Such complete opening is an advantagesince it provides patency through the main branch lumen. Moreover, theopen main vessel lumen permits optional placement of a second prosthesiswithin the main branch lumen using conventional techniques.

In a first aspect of the present invention, a prosthesis comprises aradially expansible support and at least one or often two or more frondsextending axially from an end of the support. The fronds are adapted toextend around, or “expandably circumscribe” a portion of, usually atleast one-half of the circumference of the main vessel wall at or nearthe Os when the support is implanted in the branch lumen with the frondsextending into the main lumen. By “expandably circumscribe,” it is meantthat the fronds will extend into the main body lumen after initialplacement of the support within the branch body lumen. The fronds willbe adapted to then be partially or fully radially expanded, typically byexpansion of a balloon or other expandable structure therein, so thatthe fronds deform outwardly and conform to the interior surface of themain lumen.

The fronds will usually extend axially within the main vessel lumen forsome distance after complete deployment. In certain embodiments, thecontact between the fronds and the main vessel wall will usually extendboth circumferentially (typically at least one frond may cover an arcequal to one-half or more of the circumference of the main vessel) andaxially.

Deformation of the fronds to conform to at least a portion of the wallof the main body lumen provides a generally continuous coverage of theOs from the side branch lumen to the main vessel lumen. Further and/orcomplete expansion of the fronds within the main body lumen may pressthe fronds firmly against the main body lumen wall and open up thefronds so that they do not obstruct flow through the main body lumen,while maintaining patency and coverage of the side branch and Os.

Usually, the prosthesis will include at least two or three frondsextending axially from the end of the support. The prosthesis couldinclude four, five, or even a greater number of fronds, but the use ofthree such fronds is presently contemplated for a coronary arteryembodiment. The fronds will have an initial length (i.e., prior toradial expansion of the prosthesis) which is at least about 1.5 timesthe width of the prosthesis prior to expansion, typically at least about2 times the width, more typically at least about 5 times the width, andoften about 7 times the width or greater. The lengths will typically beat least about 2 mm, preferably at least about 3 mm, and more preferablyat least about 6 mm. The frond length may also be considered relative tothe diameter of the corresponding main vessel. For example, a prosthesisconfigured for use in a branch vessel from a main vessel having a 3 mmlumen will preferably have a frond length of at least about 7 mm and insome embodiments at least about 9 mm.

Embodiments of the present invention incorporating only a single frondare also contemplated. The single frond may extend axially from thebranch vessel support as has been described in connection with multifrond embodiments. Alternatively, the single frond (or two or three ormore fronds) may extend in a helical or spiral pattern, such that itwraps in a helical winding about the longitudinal axis extending throughthe branch vessel support.

The fronds may have a fixed width or a width which is expandable toaccommodate the expansion of the support, and the fronds may be “hinged”at their point of connection to the support to permit freedom to adaptto the geometry of the main vessel lumen as the prosthesis is expanded.As used herein, “hinged” does not refer to a specific structure such asa conventional hinge, but rather to any combination of structures,materials and dimensions that permit multiaxial flexibility of the frondrelative to the support so that the frond can bend in any directionand/or rotate about any axis to conform to the abluminal surface of theexpanded main vessel stent under normal use conditions. It is alsopossible that the fronds could be attached at a single point to thesupport, thus reducing the need for such expandability. The fronds maybe congruent, i.e., have identical geometries and dimensions, or mayhave different geometries and/or dimensions. In particular, in someinstances, it may be desirable to provide fronds having differentlengths and/or different widths.

In another aspect of the invention, at least one of the of fronds has aloop or filament shape and includes a first expandable strut configuredto be positioned at the Os in an expanded state and provide radialsupport to an interior portion of the main body lumen. The fronds can befabricated from flexible metal wire, molded, laser cut or otherwiseformed from tube stock in accordance with known techniques. The strutcan be configured to be substantially triangular in the expanded state.Also, at least one of the fronds may be configured to be expandablydeployed proximate a vessel wall by an expandable device such as anexpandable balloon catheter.

In another aspect of the invention, a prosthesis delivery systemcomprises a delivery catheter having an expandable member and aprosthesis carried over the expandable member. The prosthesis has aradially expandable support such as a tubular stent and at least twofronds extending axially from the support. The system also includes aretainer for capturing the fronds to prevent them from divaricating fromthe expandable member as the catheter is advanced through a patient'svasculature. “Divarication” as used herein means the separation orbranching of the fronds away from the delivery catheter. Variousembodiments of the capture means prevent divarication by constrainingand/or imparting sufficient hoop strength to the fronds to prevent themfrom branching from the expandable member during catheter advancement inthe vasculature.

In one embodiment, the capturing means comprises a portion of theexpandable member that is folded over the fronds where the foldsprotrude through axial gaps between adjacent fronds. In anotherembodiment, the capturing means comprises a cuff that extends over atleast a portion of the fronds to hold them during catheter advancement.The cuff can be positioned at the proximal end of the prosthesis and canbe removed by expansion of the expandable member to either plasticallyor elastically deform the cuff, break the cuff, or reduce the cuff inlength axially as the cuff expands circumferentially. The cuff is thenwithdrawn from the target vessel. In yet another embodiment, thecapturing means can comprise a tether which ties together the fronds.The tether can be configured to be detached from the fronds prior toexpansion of the expandable member. In alternative embodiments, thetether can be configured to break or release upon expansion of theexpandable member so as to release the fronds.

In an exemplary deployment protocol using the prosthesis deliverysystem, the delivery catheter is advanced to position the prosthesis ata target location in a body lumen. During advancement, at least aportion of the fronds are radially constrained to prevent divaricationof the fronds from the delivery catheter. When the target location isreached, the radial constraint is released and the prosthesis isdeployed within the lumen.

In various embodiments, the release of the fronds and expansion of theprosthesis can occur simultaneously or alternatively, the radialconstraint can be released prior to, during, or afterexpanding/deploying the prosthesis. In embodiments where the radialconstraint comprises balloon folds covering the fronds or a cuff ortether, the constraint can be released as the balloon is inflated. Inalternative embodiments using a cuff or tether, the cuff/tether can bewithdrawn from the fronds prior to expansion of the support.

Embodiments of the above protocol can be used to deploy the prosthesisacross the Os of a branch body lumen and trailing into the main bodylumen. In such applications, the prosthesis can be positioned so thatthe stent lies within the branch body and at least two fronds extendinto the main body lumen. The fronds are then circumferentially deformedto conform to at least a portion of the main vessel wall to define amain vessel passage through the fronds. At least two and preferably atleast three fronds extend into the main body lumen.

Radiopaque or other medical imaging visible markers can be placed on theprostheses and/or delivery balloon at desired locations. In particular,it may be desirable to provide radiopaque markers at or near thelocation on the prosthesis where the stent is joined to the fronds. Suchmarkers will allow a transition region of the prosthesis between thestent and the fronds to be properly located near the Os prior to stentexpansion. The radiopaque or other markers for locating the transitionregion on the prosthesis can also be positioned at a correspondinglocation on a balloon catheter or other delivery catheter. Accordingly,in one embodiment of the deployment protocol, positioning the prosthesiscan include aligning a visible marker on at least one of the prosthesis,on the radial constraint, and the delivery balloon with the Os.

In various embodiments for deploying the prosthesis, the support isexpanded with a balloon catheter expanded within the support. In someinstances, the support and the fronds may be expanded and deformed usingthe same balloon, e.g., the balloon is first used to expand the support,partially withdrawn, and then advanced transversely through the frondswhere it is expanded for a second time to deform the fronds. A balloonthe length of the support (shorter than the total prosthesis length) canbe used to expand the support, and then be proximally retracted andexpanded in the fronds. Alternatively, separate balloon catheters may beemployed for expanding the support within the side branch and fordeforming the fronds against the wall of the main body lumen.

The fronds may expand radially in parallel with the support section ofthe prosthesis. Then, in a second step, the fronds may be folded out ofplane as the main vessel stent or balloon is deployed. Deformation ofthe fronds at least partially within the main body lumen provides agenerally continuous coverage of the Os from the side body lumen to themain body lumen. Further and/or complete expansion of the fronds withinthe main body lumen may press the fronds firmly against the main bodylumen wall and open up the fronds so that they do not obstruct flowthrough the main body lumen.

The prosthesis may include at least one and in some embodiments at leastthree fronds extending axially from the end of the support. The frondswill have an initial length (i.e., prior to radial expansion of thestent) which is at least about 1.5 times the cross sectional width ofthe support prior to expansion, typically at least about 2 times thewidth, more typically at least about 5 times the width, and often about7 times the width or greater. The lengths of the fronds will typicallybe at least about 2 mm, preferably at least about 3 mm, and morepreferably at least about 6 mm, as discussed elsewhere herein additionaldetail. The fronds will usually have a width which is expandable toaccommodate the expansion of the stent, and the fronds may be “hinged”or otherwise flexibly connected at their point of connection to theprosthesis to permit freedom to adapt to the geometry of the main vessellumen as the stent is expanded. It is also possible that the frondscould be attached to the single point to the prosthesis, thus reducingthe need for such expandability. Fronds may be optimized for particularbifurcation angles and orientations, such as by making the fronds forpositioning closer to the “toe” of the bifurcation longer than thefronds for positioning closer to the carina or “heel” of thebifurcation.

The fronds are configured such that during deployment and main vesselstent passage and placement, the fronds allow for longitudinalelongation or compression. In particular, the fronds may elongateaxially during main vessel stent deployment, in order to fullyaccommodate the main vessel stent as will be apparent from thedisclosure herein. The longitudinal adjustability of the fronds enablesthe implant to axially elongate or contract by at least about 5%, andoften at least about 10% of the total length of the implant, based uponits predeployed length. In some cases, the longitudinal adjustability ofthe fronds enables the implant to axially elongate or contract by atleast about 20% to about 30% of the total length of the implant, basedupon its predeployed length. In some cases, the longitudinaladjustability of the fronds enables the implant to axially elongate orcontract by at least about 30% to about 50% or more of the total lengthof the implant, based upon its predeployed length. Thus, in an implanthaving an overall length of about 19 mm prior to deployment, the axiallength of the implant as measured along the outside surface of thelongest frond post-deployment may achieve an elongation of at leastabout 1.9 mm under normal deployment conditions.

Referring now to FIGS. 1 and 2, an embodiment of a prosthesis anddelivery system 5 of the present invention for the delivery of aprosthesis to a bifurcated vessel can include a prosthesis 10 and adelivery catheter 30. Prosthesis 10 can include at least a radiallyexpansible support section 12 and a frond section 14 with one or morefronds 16. The base of the fronds resides in a transition zone,described below. In various embodiments, the frond section 14 includesat least two axially extending fronds 16, with three being illustrated.

Balloon catheters suitable for use with the prosthesis of the presentinvention are well understood in the art, and will not be described ingreat detail herein. In general, a catheter suitable for use fordeployment of the prosthesis of the present invention will comprise anelongate tubular body extending between a proximal end and a distal end.The length of the (catheter) tubular body depends upon the desiredapplication. For example, lengths in the area of from about 120 cm toabout 140 cm are typical for use in a percutaneous transluminal coronaryapplication intended for accessing the coronary arteries via the femoralartery. Other anatomic spaces including renal, iliac, femoral and otherperipheral applications may call for a different catheter shaft lengthand balloon dimensions, depending upon the vascular access site as willbe apparent to those of skill in the art.

The catheter shaft is provided with at least one central lumen, for aninflation media for inflating an inflatable balloon carried by thedistal end of the catheter shaft. In an over the wire embodiment, thecatheter shaft is additionally provided with a guidewire lumen extendingthroughout the entire length thereof. Alternatively, the prosthesis ofthe present invention may be deployed from a rapid exchange or monorailsystem, in which a proximal access port for the guidewire lumen isprovided along the side wall of the catheter shaft distally of theproximal manifold, such as within about the distal most 20 cm of thelength of the balloon catheter, or from a convertible system as is knownin the art.

The catheter shaft for most applications will be provided with anapproximately circular cross sectional configuration, having an externaldiameter within the range of from about 0.025 inches to about 0.065inches depending upon, among other things, whether the targetbifurcation is in the coronary or peripheral vasculature. Systems mayhave diameters in excess of about 0.25 inches and up to as much as about0.35 inches in certain applications. Diameters of from about 1.5 mm upto as large as about 7 mm are contemplated for coronary indications.Additional features and characteristics may be included in thedeployment catheter design, such frond retention structures discussedbelow, depending upon the desired functionality and clinical performanceas will be apparent to those of skill in the art.

The radially expansible support section 12 will typically be expandableby an expansion device such as a balloon catheter, but alternatively itcan be self expandable. The support section 12 may be formed using anyof a variety of conventional patterns and fabrication techniques as arewell-described in the prior art.

Depending upon the desired clinical result, the support section or stent12 may be provided with sufficient radial force to maintain patency of adiseased portion of the branch lumen. This may be desirable in aninstance were vascular disease is present in the branch vessel.Alternatively, the support section 12 may be simply called upon toretain the fronds in position during deployment of the primary vascularimplant. In this instance, a greater degree of flexibility is affordedfor the configuration of the wall pattern of the support section 12. Forexample, support section 12 may comprise a helical spiral, such as aNitinol or other memory metal which is deployable from an elongatedeployment lumen, but which reverts to its helical configuration withinthe branch vessel. Alternative self expandable structures may be usedsuch as a zig-zag series of struts, connected by a plurality of proximalapexes and a plurality of distal apexes and rolled into a cylindricalconfiguration. This configuration is well understood in the vasculargraft and stent arts, as a common foundation for a self expandabletubular support.

In one implementation of the present invention, the prosthesis comprisesan overall length of about 19 mm, which is made up of a stent having alength of about 9.6 mm, a targeted expanded diameter of about 2.5 mm anda plurality of fronds having a length of about 9.3 mm.

The fronds will usually have a width measured in a circumferentialdirection in the transition zone which is expandable from a first,delivery width to a second, implanted width to accommodate the expansionof the support, while maintaining optimal wall coverage by the fronds.Thus, although each of the fronds may comprise a single axiallyextending ribbon or strut, fronds are preferably configured to permitexpansion in a circumferential direction at least in the transition zonewith radial expansion of the support structure. For this purpose, eachfrond may comprise a single axially extending element, but oftencomprises at least two axially extending elements 66A and 66D, andoptimally three or more axially extending elements, which can be spacedlaterally apart from each other upon radial expansion of the prosthesis,to increase in width in the circumferential direction. The increasedwidth referred to herein will differ on a given frond depending uponwhere along the length of the frond the measurement is taken. Fronds ofthe type illustrated herein will increase in width the most at the endattached to the support, and the least (or none) at the free apex end aswill be appreciated by those of skill in the art. Circumferentiallyexpanding at least the base of the frond enables optimal wall coveragein the vicinity of the ostium, following deployment of the prosthesis atthe treatment site. In addition, multiple elements results in a greatersurface area as a biological substrate or increased delivery of pharmaagents.

In the illustrated embodiments, each of the fronds 16 has an equal widthwith the other fronds 16. However, a first frond or set of fronds may beprovided with a first width (measured in a circumferential direction)and a second frond or set of fronds may be provided with a second,different width. Dissimilar width fronds may be provided, such asalternating fronds having a first width with fronds having a secondwidth.

In each of the foregoing constructions, radially symmetry may exist suchthat the rotational orientation of the prosthesis upon deployment isunimportant. This can simplify the deployment procedure for theprosthesis. Alternatively, prostheses of the present inventionexhibiting radial asymmetry may be provided, depending upon the desiredclinical performance. For example, a first frond or set of fronds may becentered around 0° while a second frond or set of fronds is centeredaround 180° when the prosthesis is viewed in a proximal end elevationalview. This may be useful if the fronds are intended to extend aroundfirst and second opposing sides of the main vessel stent. Asymmetry inthe length of the fronds may also be accomplished, such as by providingfronds at a 0° location with a first length, and fronds at 180° locationwith a second length. As will become apparent below, such as byreference to FIG. 9A, certain fronds in the deployed prosthesis willextend along an arc which aligns with the axis of the branch vessel at adistal end, and aligns with the axis of the main vessel at a proximalend. The proximal ends of fronds of equal length will be positionedaxially apart along the main vessel lumen. If it is desired that theproximal ends of any of the fronds align within the same transversecross section through the main vessel lumen, or achieve another desiredconfiguration, fronds of different axial lengths will be required aswill become apparent to those of skill in the art.

Certain additional features may be desirable in the prosthesis and/ordeployment system of the present invention, in an embodiment in whichthe rotational orientation of the prosthesis is important. For example,the catheter shaft of the deployment system preferably exhibitssufficient torque transmission that rotation of the proximal end of thecatheter by the clinician produces an approximately equal rotation atthe distal end of the catheter. The torque transmission characteristicsof the catheter shaft may be optimized using any of a variety ofstructures which are known in the art. For example, a helical windingmay be incorporated into the wall of the catheter shaft, using any of avariety of embedding techniques, or by winding a filament around aninner tube and positioning an outer tube over the winding, subsequentlyheat shrinking or otherwise fusing the tubes together. Bi-directionaltorque transmission characteristics can be optimized by providing afirst winding in a first (e.g. clockwise) direction, and also a secondwinding in a second (e.g. counter clockwise) direction. The winding maycomprise any of a variety of materials, such as metal ribbon, or apolymeric ribbon. Various tubular meshes and braids may also beincorporated into the catheter wall.

In addition, the rotational orientation of the prosthesis is preferablyobservable fluoroscopically, or using other medical imaging techniques.For this purpose, one or more markers is preferably provided on eitherthe prosthesis, the restraint or the deployment catheter, to enablevisualization of the rotational orientation.

The sum of the widths measured in the circumferential direction of thefronds 16 when the prosthesis is in either the first, transluminalnavigation configuration or the second, deployed configuration willpreferably add up to no more than one circumference of the stent portionof the prosthesis. In this manner, the width of the frond 16 s at thelevel of attachment may be maximized, but without requiring overlapespecially in the first configuration. The width of each frond 16 maygenerally increase upon deployment of the prosthesis to at least about125%, often at least about 200%, and in some instances up to about 300%or more of its initial width, at least at the distal end (base) of thefrond 16. The proximal free end of each frond 16 may not increase incircumferential width at all, with a resulting gradation of increase incircumferential width throughout the axial length from the proximal endto the distal end of the frond. While portions of the fronds may expandas described above, in alternate constructions, the fronds may have awidth that remains constant or substantially constant throughout thelength of the frond as the prosthesis is deployed.

The fronds may be “hinged” as has been described at their point ofconnection to the support to permit freedom to adapt to the geometry ofthe main vessel lumen as the prosthesis is expanded. It is also possiblethat each frond is attached at a single point to the support, thusreducing the need for such expandability at the junction between thefrond and the support. The fronds may be congruent, i.e., have identicalgeometries and dimensions, or may have different geometries and/ordimensions. Again, further description of the fronds may be found inco-pending application Ser. No. 10/807,643.

Fronds 16, will usually extend axially from the support section 12, asillustrated, but in some circumstances the fronds can be configured toextend helically, spirally, in a serpentine pattern, or otherconfigurations as long as the configuration permits placement of thestent in a vessel such that the fronds extend across the Os. It isdesirable, however, that the individual fronds be radially separable sothat they can be independently, displaced, folded, bent, rotated abouttheir longitudinal axes, and otherwise positioned within the main bodylumen after the support section 12 has been expanded within the branchbody lumen. In the schematic embodiment of FIG. 1, the fronds 16 may beindependently folded out in a “petal-like” configuration, forming petals16 p, as generally shown in broken line for one of the fronds in FIGS. 1and 2.

In preferred embodiments, fronds 16 will be attached to the supportsection 12 such that they can both bend and rotate relative to an axis Athereof, as shown in broken line in FIG. 1A. Bending can occur radiallyoutwardly and rotation or twisting can occur about the axis A or aparallel to the axis A as the fronds are bent outwardly. Such freedom ofmotion can be provided by single point attachment joints as well as twopoint attachments or three or more point attachments.

Referring now to FIG. 2A, an exemplary embodiment of a prosthesis 50(shown in a “rolled out” pattern) comprises a support or stent section52 and a frond section 54. Support section 52 comprises a firstplurality of radially expansible serpentine elements 56 which extendcircumferentially to form a cylindrical ring having a plurality of openareas or cells 57 therein. The cylindrical rings formed by serpentineelements 56 are coaxially aligned along the longitudinal axis of thesupport section 52, and, in the illustrated embodiment, alternate with asecond plurality of cylindrical rings formed by radially expandableserpentine elements 58 defining a second set of smaller cells 59. Strutcoverage in the range of from about 10% to about 20%, and in someembodiments between about 16%-18% by area is contemplated. A pluralityof spaced apart, axially extending struts 61 connect adjacent rings. Theparticular pattern illustrated for this structure is well-known andchosen to be exemplary of a useful prosthesis. It will be appreciatedthat a wide variety of other conventional stent structures and patternsmay be equally useful as the support section of the prostheses of thepresent invention. See, for example, FIGS. 2B-2F.

The wall patterns can be varied widely as desired to provide additionalcoverage, transition in axial stiffness, and accommodate various sidebranch angles with respect to the main vessel long axis as well asostial geometries, i.e., diameter and shape.

The support section 52 is joined to the frond section 54 at a pluralityof points 65 along a transition line or zone 60. Individual fronds 16,comprise a circumferentially expandable wall pattern. In the embodimentillustrated in FIG. 2A, each frond comprises four curving elements 66 atthe distal end of the transition zone 60, which reduce in number tothree and then to two in the axial (proximal) direction away from thestent 52. The particular structures shown illustrate one example of away to achieve circumferential expansion of the individual fronds as theprosthesis is expanded. This is accomplished since each frond isattached to three adjacent serpentine ring apexes 63 in the proximalmost serpentine ring 56. Thus, as these serpentine rings 56 areexpanded, the circumferential distance between adjacent apexes 63 willincrease, thereby causing each frond to “widen” by expanding in acircumferential direction. It would be possible, of course, to join eachof the fronds 16 only at a single location to the prosthesis 52, thusallowing the anchors to be deployed without radial expansion. Two orfour or more points of attachment may also be used, depending upon thewall pattern and desired performance of the resulting prosthesis. Thestruts in the transition section are designed to “cup” with adjacentstruts such that the gap formed within and between fronds in theexpanded prosthesis is minimized.

The circumferentially expandable fronds are curved about thelongitudinal axis of the prosthesis and have a number of hinge regionswhich increase their conformability upon circumferential expansion by aballoon, as described hereinafter. Such conformability is desirablesince the fronds will be expanded under a wide variety of differinganatomical conditions which will result in different final geometriesfor the fronds in use. The final configuration of the fronds in the mainvessel lumen will depend on a number of factors, including length of thefronds and geometry of the vasculature and will vary greatly fromdeployment to deployment. While the fronds together will cover at leasta portion of the main vessel wall circumference, most fronds will alsobe deformed to cover an axial length component of the main vessel wallas well. Such coverage is schematically illustrated in the figuresdiscussed below.

In other embodiments, prosthesis structure 50 can include four or fiveor six or more fronds 16. Increasing the number of fronds provides anincreased number of anchor points between a branch vessel stent and amain vessel stent. This may serve to increase the mechanical linkagebetween stent 10 and another stent deployed in an adjacent vessel. Invarious embodiments, fronds 16 can be narrower (in width) thanembodiments having few fronds so as to increase the flexibility of thefronds. The increased flexibility can facilitate the bending of thefronds during stent deployment including bending from the branch bodylumen into the main body lumen.

Referring now to FIG. 2B, in various embodiments, fronds 16 can comprisethin filaments formed into loops 17. An exemplary embodiment of aprosthesis structure 50 having a plurality of filament loops 17 is shownin FIG. 2B in a rolled out pattern. In various embodiments filamentloops 17 can have at least one or two or more intra-filament connectors18, 19 which extend in a circumferential direction to connect twoadjacent filaments defining a filament loop 17. Connectors 18, 19preferably include at least one nonlinear undulation such as a “U”, “V”or “W” or “S” shape to permit radial expansion of the prosthesis in thevicinity of the fronds. (The intra-filament space may be crossed with aballoon catheter and dilated to larger diameters).

The illustrated embodiment includes a first intra-filament connector 18in the transition area 60 for each frond 16, and a second connector 19positioned proximally from the first connector 18. One or both of thefirst and second connectors 18, 19 can be configured to expand orotherwise assume a different shape when the fronds are deployed. Atleast five or ten or 20 or more connectors 18, 19 may be providedbetween any two adjacent filaments 66 depending upon the desiredclinical performance. Also connectors 18, 19 can be continuous withfrond loops 17 and have substantially the same cross sectional thicknessand/or mechanical properties. Alternatively, connectors 18, 19 can havedifferent diameters and/or mechanical properties (e.g. one or more ofincreased elasticity, elastic limit, elongation, stiffness etc.) and orbiological properties (surface finish, passivation, coatings, etc.). Inone embodiment the distal connector 18 can be stiffer than the proximalconnector 19 so as to allow more flexibility at the proximal tip of thefronds.

Connectors 18 and 19 can be further configured to perform severalfunctions. First, to act as mechanical struts to increase the stiffness(e.g. longitudinal, torsional, etc) of the filament fronds 16. Second,when the fronds are deployed, connectors 18 and 19 can be designed toassume a deployed shape which provides radial mechanical support (e.g.act as prosthesis) to the target vessel including at the Os. This isparticularly the case for first connector 18 which can be configured tounfurl in the circumferential direction and assume a semi-triangularshape in its deployed state with an expansion axis (of the connectedpoints of the triangle to fronds) substantially parallel to the radialaxis of the vessel. This configuration of connector 18 serves to provideradial mechanical support as well as coverage at the Os in particular.Connector 18 can also be configured to assume other deployed shapes aswell, such as semi-circular etc. The number and spacing and deployedshape of the connectors 18 can be configured to provide the same amountor density at the Os (e.g. number of struts per axial or radial lengthof tissue) as the stent region 52 of the prosthesis provides to the restof the vessel. In general, by varying the dimensions and number of thefilaments 66 and connectors 18 any of a variety of physical propertiescan be achieved. The connectors 18 and 19 and filaments 66 may beselected and designed to cooperate to provide maximum area coverage,and/or maximum mechanical radial force, or either objective without theother. The number of filaments can be in the range of from about 3 toabout 30, with specific embodiments of 4, 6, 10, 20 and 25.

In various embodiments, the arrangement of the filaments fronds can beconfigured to provide several functions. First, as described above theycan be configured to provide increased coverage and hence patency of theOs by having an increased number of mechanical support points in the Osand hence a more even distribution of force (e.g. radial force) on thefronds. Also, for embodiments of drug coated stents, including drugeluting stents they provide an increased amount of surface area for theelution of the drug. This in turn, serves to provide increased and/ormore constant local concentration of the selected drug at the vesselwall and/or other target site. Other pharmacokinetic benefits can beobtained as well, such as a more constant drug release rate. For stentscoated with anti-cell proliferative, anti-inflammatory and/or anti-cellmigration drugs such as Taxol (paclitaxel), Rapamycin and theirderivatives, the use of high filament type fronds serve as a means toreduce the incidence and rate of hyperplasia and restenosis. Similarresults can be obtained with other drugs known in the art for reducingrestenosis (e.g. anti-neo-plastics, anti-inflammatory drugs, etc.). Alsoin a related embodiment the filament fronds can be coated with adifferent drug and/or a different concentration of drug as the remainderof the stent. In use, such embodiment can be configured to provide oneor more of the following: i) a more constant release rate of drug; ii)bimodal release of drug; iii) multi drug therapies; and iv) titration ofdrug delivery/concentration for specific vessels and/or release rates.As disclosed in additional detail below, the drug may be incorporatedinto a biostable, biodegradable, or bioerodable polymer matrix, and maybe optimized for long-term pharma release (prophylactic local drugdelivery).

In general, in any of the embodiments herein, the prosthesis of thepresent invention can be adapted to release an agent for prophylactic oractive treatment from all or from portions of its surface. The activeagents (therapy drug or gene) carried by the prosthesis may include anyof a variety of compounds or biological materials which provide thedesired therapy or desired modification of the local biologicalenvironment. Depending upon the clinical objective in a givenimplementation of the invention, the active agent may includeimmunosuppressant compounds, anti-thrombogenic agents, anti-canceragents, hormones, or other anti-stenosis drugs. Suitableimmunosuppressants may include ciclosporinA (CsA), FK506,DSG(15-deoxyspergualin, 15-dos), MMF, rapamycin and its derivatives,CCI-779, FR 900520, FR 900523, NK86-1086, daclizumab, depsidomycin,kanglemycin-C, spergualin, prodigiosin25-c, cammunomicin, demethomycin,tetranactin, tranilast, stevastelins, myriocin, gliotoxin, FR 651814,SDZ214-104, bredinin, WS9482, and steroids. Suitable anti-thrombogenicdrugs may include anti-platelet agents (GP IIb/IIIa, thienopyridine,GPIb-IX, ASA, etc and inhibitors for the coagulation cascade (heparin,hyrudin, thrombin inhibitors, Xa inhibitors, VIIa Inhibitors, TissueFactor Inhibitors and the like) Suitable anti-cancer (antiproliferative) agents may include methotrexate, purine, pyridine, andbotanical (e.g. paclitaxel, colchicines and triptolide), epothilone,antibiotics, and antibodies. Suitable additional anti-stenosis agentsinclude batimastat, NO donor, 2-chlorodeoxyadenosine, 2-deoxycoformycin,FTY720, Myfortic, ISA (TX) 247, AGI-1096, OKT3, Medimmune, ATG, Zenapax,Simulect, DAB486-IL-2, Anti-ICAM-1, Thymoglobulin, Everolimus, Neoral,Azathioprine (AZA), Cyclophosphamide, Methotrexate, Brequinar Sodium,Leflunomide, or Mizoribine. Gene therapy formulations include Keratin 8,VEGF, and EGF, PTEN, Pro-UK, NOS, or C-myc may also be used.

Any of the coatings described herein may be provided on either thelumenal surface, the abluminal surface, or both, on the prosthesisdisclosed herein. In addition, coatings may be provided on only thesupport portion, only the frond portion, only the transition portion, orany combination thereof, depending upon the desired clinicalperformance. In addition to the coatings described above, at least aportion of the prosthesis may be provided with a coating which rendersthe implant compatible for in vivo attachment and proliferation of cellson the surface thereof. This coating is preferably provided on theabluminal surface of the implant, and may be omitted from the lumenalsurface of the implant. In general, the coating may comprise atherapeutically effective amount of an antibody which reacts with anendothelial cell surface antigen, to facilitate cellular proliferationon the surface of the implant. Additional details of antibody coatingsto promote endothelial cell adherence may be found in U.S. Pat. No.7,037,332, entitled Medical Device with Coating that PromotesEndothelial Cell Adherence, issued May 2, 2006 to Kutryk, et al., thedisclosure of which is incorporated in its entirety herein by reference.

Methods of preventing restenosis include inhibiting VSMC hyperplasia ormigration, promoting endothelial cell growth, or inhibiting cell matrixproliferation with the delivery of suitable compounds from theprosthesis. Radiation, systemic drug therapy and combinations of theforegoing may also be used. The desired dose delivery profiles for theforegoing are in some cases reported in the literature, or may beoptimized for use with the prosthesis of the present invention throughroutine experimentation by those of skill in the art in view of thedisclosure herein.

Binding systems (e.g., chemical binding, absorbable and non absorbablepolymeric coatings) for releasably carrying the active agent with theprosthesis are well known in the art and can be selected to cooperatewith the desired drug elution profile and other characteristics of aparticular active agent as will be appreciated by those of skill in theart.

In general, the drug(s) may be incorporated into or affixed to the stentin a number of ways and utilizing any biocompatible materials; it may beincorporated into e.g. a polymer or a polymeric matrix and sprayed ontothe outer surface of the stent. A mixture of the drug(s) and thepolymeric material may be prepared in a solvent or a mixture of solventsand applied to the surfaces of the stents also by dip-coating, brushcoating and/or dip/spin coating, the solvent (s) being allowed toevaporate to leave a film with entrapped drug(s). In the case of stentswhere the drug(s) is delivered from micropores, struts or channels, asolution of a polymer may additionally be applied as an outlayer tocontrol the drug(s) release; alternatively, the active agent may becomprised in the micropores, struts or channels and the active co-agentmay be incorporated in the outlayer, or vice versa. The active agent mayalso be affixed in an inner layer of the stent and the active co-agentin an outer layer, or vice versa. The drug(s) may also be attached by acovalent bond, e.g. esters, amides or anhydrides, to the stent surface,involving chemical derivatization. The drug(s) may also be incorporatedinto a biocompatible porous ceramic coating, e.g. a nanoporous ceramiccoating. The medical device of the invention is configured to releasethe active co-agent concurrent with or subsequent to the release of theactive agent.

Examples of polymeric materials known for this purpose includehydrophilic, hydrophobic or biocompatible biodegradable materials, e.g.polycarboxylic acids; cellulosic polymers; starch; collagen; hyaluronicacid; gelatin; lactone-based polyesters or copolyesters, e.g.polylactide; polyglycolide; polylactide-glycolide; polycaprolactone;polycaprolactone-glycolide; poly(hydroxybutyrate);poly(hydroxyvalerate); polyhydroxy (butyrate-co-valerate);polyglycolide-co-trimethylene carbonate; poly(dioxanone);polyorthoesters; polyanhydrides; polyaminoacids; polysaccharides;polyphospoeters; polyphosphoester-urethane; polycyanoacrylates;polyphosphazenes; poly(ether-ester) copolymers, e.g. PEO-PLLA, fibrin;fibrinogen; or mixtures thereof; and biocompatible non-degradingmaterials, e.g. polyurethane; polyolefins; polyesters; polyamides;polycaprolactam; polyimide; polyvinyl chloride; polyvinyl methyl ether;polyvinyl alcohol or vinyl alcohol/olefin copolymers, e.g. vinylalcohol/ethylene copolymers; polyacrylonitrile; polystyrene copolymersof vinyl monomers with olefins, e.g. styrene acrylonitrile copolymers,ethylene methyl methacrylate copolymers; polydimethylsiloxane;poly(ethylene-vinylacetate); acrylate based polymers or copolymers, e.g.polybutylmethacrylate, poly(hydroxyethyl methylmethacrylate); polyvinylpyrrolidinone; fluorinated polymers such as polytetrafluoroethylene;cellulose esters e.g. cellulose acetate, cellulose nitrate or cellulosepropionate; or mixtures thereof.

When a polymeric matrix is used, it may comprise multiple layers, e.g. abase layer in which the drug(s) is/are incorporated, e.g.ethylene-co-vinylacetate and polybutylmethacrylate, and a top coat, e.g.polybutylmethacrylate, which is drug(s)-free and acts as adiffusion-control of the drug(s). Alternatively, the active agent may becomprised in the base layer and the active co-agent may be incorporatedin the outlayer, or vice versa. Total thickness of the polymeric matrixmay be from about 1 to 20μ or greater.

The drug(s) elutes from the polymeric material or the stent over timeand enters the surrounding tissue, e.g. up to ca. 1 month to 10 years.The local delivery according to the present invention allows for highconcentration of the drug(s) at the disease site with low concentrationof circulating compound. The amount of drug(s) used for local deliveryapplications will vary depending on the compounds used, the condition tobe treated and the desired effect. For purposes of the invention, atherapeutically effective amount will be administered; for example, thedrug delivery device or system is configured to release the active agentand/or the active co-agent at a rate of 0.001 to 200 μg/day. Bytherapeutically effective amount is intended an amount sufficient toinhibit cellular proliferation and resulting in the prevention andtreatment of the disease state. Specifically, for the prevention ortreatment of restenosis e.g. after revascularization, or antitumortreatment, local delivery may require less compound than systemicadministration. The drug(s) may elute passively, actively or underactivation, e.g. light-activation.

A possible alternative to a coated stent is a stent containing wells orreservoirs that are loaded with a drug, as discussed by Wright et al.,in “Modified Stent Useful for Delivery of Drugs Along Stent Strut,” U.S.Pat. No. 6,273,913, issued Aug. 14, 2001; and Wright et al., in “Stentwith Therapeutically Active Dosage of Rapamycin Coated Thereon,” USpatent publication US 2001/0027340, published Oct. 4, 2001, thedisclosures of both of which are incorporated in their entireties hereinby reference.

Wright et al. in U.S. Pat. No. 6,273,913, describes the delivery ofrapamycin from an intravascular stent and directly from microporesformed in the stent body to inhibit neointimal tissue proliferation andrestenosis. The stent, which has been modified to contain micropores, isdipped into a solution of rapamycin and an organic solvent, and thesolution is allowed to permeate into the micropores. After the solventhas been allowed to dry, a polymer layer may be applied as an outerlayer for a controlled release of the drug.

U.S. Pat. No. 5,843,172 by Yan, which is entitled “Porous MedicatedStent”, discloses a metallic stent that has a plurality of pores in themetal that are loaded with medication. The drug loaded into the pores isa first medication, and an outer layer or coating may contain a secondmedication. The porous cavities of the stent can be formed by sinteringthe stent material from metallic particles, filaments, fibers, wires orother materials such as sheets of sintered materials.

Leone et al. in U.S. Pat. No. 5,891,108 entitled “Drug Delivery Stent”describes a retrievable drug delivery stent, which is made of a hollowtubular wire. The tubular wire or tubing has holes in its body fordelivering a liquid solution or drug to a stenotic lesion. Brown et al.in “Directional Drug Delivery Stent and Method of Use,” U.S. Pat. No.6,071,305 issued Jun. 6, 2000, discloses a tube with an eccentric innerdiameter and holes or channels along the periphery that house drugs andcan deliver them preferentially to one side of the tube. Scheerder etal. in US patent publication US 2002/0007209, discloses a series ofholes or perforations cut into the struts on a stent that are able tohouse therapeutic agents for local delivery.

Referring to the patent literature, Heparin, as well as otheranti-platelet or anti-thrombolytic surface coatings, have been reportedto reduce thrombosis when carried by the stent surface. Stents includingboth a heparin surface and an active agent stored inside of a coatingare disclosed, for example, in U.S. Pat. Nos. 6,231,600 and 5,288,711.

A variety of agents specifically identified as inhibiting smoothmuscle-cell proliferation, and thus inhibit restenosis, have also beenproposed for release from endovascular stents. As examples, U.S. Pat.No. 6,159,488 describes the use of a quinazolinone derivative; U.S. Pat.No. 6,171,609, describes the use of taxol, and U.S. Pat. No. 5,716,981,the use of paclitaxel, a cytotoxic agent thought to be the activeingredient in the agent taxol. The metal silver is cited in U.S. Pat.No. 5,873,904. Tranilast, a membrane stabilizing agent thought to haveanti-inflammatory properties is disclosed in U.S. Pat. No. 5,733,327.

More recently, rapamycin, an immunosuppressant reported to suppress bothsmooth muscle cell and endothelial cell growth, has been shown to haveimproved effectiveness against restenosis, when delivered from a stent.See, for example, U.S. Pat. Nos. 5,288,711 and 6,153,252. Also, in PCTPublication No. WO 97/35575, the monocyclic triene immunosuppressivecompound everolimus and related compounds have been proposed fortreating restenosis, via systemic delivery.

Any one or a combination of the frond section, support section andtransition may comprise a bioabsorbable material, which will degrade orotherwise dissipate over time. The bioabsorbable implant may be aconvenient platform for the elution of any of a variety of biologicallyactive agents, such as those identified above.

Prostheses in accordance with the present invention may comprise any ofa variety of bioabsorbable polymers, depending upon the desiredperformance. These may include poly(alpha-hydroxy acid) such aspolylactide [poly-L-lactide (PLLA), poly-D-lactide (PDLA)],polyglycolide (PGA), polydioxanone, polycaprolactone, polygluconate,polylactic acid-polyethylene oxide copolymers, poly(hydroxybutyrate),polyanhydride, polyphosphoester, poly(amino acids), or relatedcopolymers materials, each of which have a characteristic degradationrate in the body. For example, PGA and polydioxanone are relativelyfast-bioabsorbing materials (weeks to months) and PLA andpolycaprolactone are relatively slow-bioabsorbing material (months toyears).

Bioabsorbable PLLA and PGA material are degraded in vivo throughhydrolytic chain scission to lactic acid and glycolic acid,respectively, which in turn is converted to CO.sub.2 and then eliminatedfrom the body by respiration. Heterogeneous degradation ofsemicrystalline polymers occurs due to the fact that such materials haveamorphous and crystalline regions. Degradation occurs more rapidly atamorphous regions than at crystalline regions. This results in theproduct decreasing in strength faster than it decreases in mass. Totallyamorphous, cross-linked polyesters show a more linear decrease instrength with mass over time as compared to a material with crystallineand amorphous regions. Degradation time may be affected by variations inchemical composition and polymer chain structures, and materialprocessing.

Controlled release of a drug, via a bioabsorbable polymer, offers tomaintain the drug level within the desired therapeutic range for theduration of the treatment. In the case of stents, the prosthesismaterials may be selected to maintain vessel support for at least abouttwo weeks or until incorporated into the vessel wall even withbioabsorbable, biodegradable polymer constructions.

Several polymeric compounds that are known to be bioabsorbable andhypothetically have the ability to be drug impregnated may be useful inprosthesis formation herein. These compounds include: poly-1-lacticacid/polyglycolic acid, polyanhydride, and polyphosphate ester. A briefdescription is provided below.

Poly-1-lactic acid/polyglycolic acid has been used for many years in thearea of bioabsorbable sutures. It is currently available in many forms,i.e., crystals, fibers, blocks, plates, etc. These compounds degradeinto non-toxic lactic and glycolic acids. There may, however, be severalproblems with this compound. The degradation artifacts (lactic acid andglycolic acid) are slightly acidic. The acidity can cause minorinflammation in the tissues as the polymer degrades. This sameinflammation could be detrimental in coronary and peripheral arteries,i.e., vessel occlusion. Another potential problem associated with thispolymer is the ability to control and predict the degradation behavior.It does not appear possible for the biochemist to accurately predictdegradation time, which could be detrimental for a drug delivery deviceif dosing parameters need to be tightly controlled.

Other compounds which could be used are the polyanhydrides. They arecurrently being used with several chemotherapy drugs for the treatmentof cancerous tumors. These drugs are compounded into the polymer whichis molded into a cube-like structure and surgically implanted at thetumor site.

Polyanhydrides have weaknesses in their mechanical properties, due tolow molecular weights. This drawback may make them difficult to processinto a filament form such as for the fronds or transition section of theprostheses disclosed herein. Also, polyanhydrides have relatively poorsolubility, making characterization and fabrication difficult.

A third class of compounds which may be preferred includes polyphosphateesters. Polyphosphate ester is a compound such as that disclosed in U.S.Pat. Nos. 5,176,907; 5,194,581; and U.S. Pat. No. 5,656,765 issued toLeong which are incorporated herein by reference. The polyphosphateesters have high molecular weights (600,000 average), yieldingattractive mechanical properties. This high molecular weight leads totransparency, and film and fiber properties. It has also been observedthat the phosphorous-carbon-oxygen plasticizing effect, which lowers theglass transition temperature, makes the polymer desirable forfabrication.

The basic structure of polyphosphate ester monomer is shown below.

where

P corresponds to Phosphorous,

O corresponds to Oxygen,

and R and R1 are functional groups.

Reaction with water leads to the breakdown of this compound intomonomeric phosphates (phosphoric acid) and diols (see below).

It is the hydrolytic instability of the phosphorous ester bond whichmakes this polymer attractive for controlled drug release applications.A wide range of controllable degradation rates can be obtained byadjusting the hydrophobicities of the backbones of the polymers and yetassure biodegradability.

The functional side groups allow for the chemical linkage of drugmolecules to the polymer. This is shown below.

The drug may also be incorporated into the backbone of the polymer.

The highly hydrolytically reactive phosphorous ester bond, the favorablephysical properties, and the versatile chemical structure may make thepolyphosphate esters a superior drug delivery system for a prosthesis.See U.S. Pat. No. 5,545,208 to Wolff, the disclosure of which isincorporated in its entirety herein by reference.

Use of multiple filaments per frond also provides for a more openstructure of the fronds section 54 of the prosthesis to allow for aneasier and less obstructed passage of a guide wire and/or the deploymentballoon by and/or through the fronds (e.g., during un-jailing proceduresknown in the art). Similarly, use of the flexible filaments also allowsthe main vessel to track between fronds and engage the main vesselstent. In particular, the thinner frond filaments facilitate advancementof the fronds over the circumference and/or the length of a main vesselstent during deployment of the fronds or the main vessel stent.Moreover, the filaments can be configured to be easily withdrawn andthen re-advanced again to allow for repositioning of either of thebranch vessel stent. Other means for facilitating advancement of themain vessel stent between the fronds can include tapering the frondsand/or coating the fronds with a lubricous coating such as PTFE orsilicone (this also facilitates release of the fronds from constrainingmeans described herein). Finally, by having an increased number offilaments, the mechanical support of the Os is not compromised if one ormore filaments should become pushed aside during the stent deployment.That is, the remaining filaments provide sufficient support of the Os tomaintain it patency. In these and related embodiments, it may bedesirable to have at least six loops 17 each comprising at least onefilament looped back upon itself at its proximal limit to provide atleast two elements per frond.

Various embodiments of the fronds can be configured to provide anincreased amount of mechanical linkage between the fronds and the mainvessel stent. In general, the frond design seeks to 1) track to site, 2)allow for advancement of MV Stent 3) increase frond-MV stent interactionand 4) frond MV wall interactions. Another means includes increasing thenumber of fronds to provide an increased number of anchor points betweena branch vessel stent and a main vessel stent. This in turn provides anincreased amount of mechanical linkage between the two stents such thatthey increasingly operate mechanically as one structure rather than twoafter deployment. This also serves to improve the spatial stability ofthe deployed stents within both vessels. That is, there is reducedmovement (e.g., axial or radial) or reduced possibility of movement ofone or both stents within their respective vessels. In particular, thelinkage serves to provide radial strength of the structure in theostium.

Referring now to FIG. 2C in an alternative embodiment of a prosthesis 50having filament fronds 17, one or two or more frond can be a shortenedfrond 16 s. That is a frond that is shortened in the longitudinaldirection. In the illustrated embodiment, shortened fronds 16 s and fulllength fronds 16 alternate around the circumference of the stent. Theamount of shortening can range from 10% to 99%. In a preferredembodiment, fronds 16 s are shortened by approximately slightly lessthan 50% in length from the length of un-shortened fronds 16.Embodiments having shortened fronds, reduce the likelihood of resistancewhen the main vessel stent 150 is positioned. Shortened fronds 16 s alsocan be configured to act more like point contacts on the main vesselstent 150 and should therefore be less likely to be swept towards the Osby deployment and/or misalignment of the main vessel stent anddeployment balloon. Also, use of less material in the fronds tends toproduce less displacement of the fronds even if the main vessel stent orballoon catches multiple fronds, and may produce a lower biologicalreaction (less foreign material).

FIGS. 2D and 2E illustrate an alternative side wall patterns for thetransition portion of the prosthesis of the present invention, on stentshaving two different side wall patterns. As described previously, thespecific stent or other support structure configuration may be variedconsiderably within the context of the present invention.

In each of the embodiments of FIGS. 2D and 2E, the struts 70 at thefrond root (e.g. transition zone) are provided with an interdigitatingor nesting configuration. In this configuration, as viewed in the flat,laid out view as in FIGS. 2D and 2E, a plurality of struts 70 extendacross the transition zone. A distal segment 72 of each strut 70inclines laterally in a first direction, to an apex 74, and theninclines laterally in a second direction to a point that may beapproximately axially aligned with a distal limit of the distal segment72. The extent of lateral displacement of the strut between its originand the apex 74 is greater than the distance between adjacent struts,when in the unexpanded configuration. In this manner, adjacent strutsstack up or nest within each other, each having a concavity 78 facing ina first lateral direction and a corresponding convexity 80 in a secondlateral direction. This configuration seeks to optimize vessel wallcoverage at the ostium, when the stent is expanded.

The axial length of each frond is at least about 10%, often at leastabout 20%, and in some embodiments at least about 35% or 75% or more ofthe length of the overall prosthesis. Within this length, adjacentfronds may be constructed without any lateral interconnection, tooptimize the independent flexibility. The axially extending component ofthe frond may be provided with an undulating or serpentine structure 82,which helps enable the fronds to rotate out of the plane when the mainvessel stent is deployed. Circumferential portions of the undulatingfronds structure make the frond very flexible out of the plane of thefrond for trackability. A plurality of connectors 84 are providedbetween parallel undulating filaments 86, 88 of each frond, to keep thefrond from being overly floppy and prone to undesirable deformation.Each of the fronds in the illustrated embodiment has a broad (i.e.relatively large radius) frond tip 90, to provide an atraumatic tip tominimize the risk of perforating the arterial or other vascular wall.

The interdigitating construction in the transition zone, as well as theundulating pattern of the frond sections both provides optimal coverageat the ostium, and provides additional strut length extension orelongation capabilities, which may be desirable during the implantationprocess.

It may also be desirable to vary the physical properties of thefilaments 86, 88, or elsewhere in the prosthesis, to achieve desiredexpansion results. For example, referring to FIG. 2E, each frond 16includes a first filament 92, attached at a first attachment point 94and a second filament 96 attached at a second attachment point 98 to thestent. A third filament 100 and a fourth filament 102 are connected tothe stent at an intermediate attachment point 104. As illustrated, thetransverse width of the third and fourth filaments 100 and 102 are lessthan the transverse width of the first and second filaments 92, 96. Thethinner filaments 100, 102 provide less resistance to expansion, andhelp maintain optimal coverage in the vicinity of the ostium uponexpansion of the prosthesis.

In any of the embodiments described herein, the fronds may be consideredto have a lumenal surface at least a portion of which will be in contactwith an outside surface of the main vessel stent, and an abluminalsurface which will be pressed into contact with the vascular wall by themain vessel stent. The lumenal and abluminal surfaces of the fronds maybe provided with similar or dissimilar characteristics, depending uponthe desired performance. For example, as described elsewhere herein, thefrond and particularly the abluminal surface may be provided with a drugeluting characteristic.

It may also be desirable to modify the lumenal surface of the frond, toenhance the physical interaction with the main vessel stent. For thispurpose, the lumenal surface of the frond may be provided with any of avariety of friction enhancing surface characteristics, or engagementstructures for engaging the main vessel stent. Friction enhancingsurfaces may comprise the use of polymeric coatings, or mechanicalroughening such as laser etching, chemical etching, sputtering, or otherprocesses. Alternatively, any of a variety of radially inwardlyextending hooks or barbs may be provided, for engaging the main vesselstent. Preferably, any radially inwardly extending hooks or barbs willhave an axial length in the radial direction of no greater thanapproximately the wall thickness of the main vessel stent strut, tominimize the introduction of blood flow turbulence. Although a varietyof main vessel stents are available, the inventors presently contemplatewall thicknesses for the struts of such main vessel stents to be on theorder of about 0.003 to 0.0055 inches for native coronary indications.Any of the foregoing surfaces textures or structures may also beprovided on the abluminal surface of the main vessel stent, to cooperatewith corresponding textures or structures on the fronds, to enhance thephysical integrity of the junction between the two, and potentiallyreduce the risk for vessel perforation by fronds.

As will be described in additional detail in connection with the method,below, proper positioning of the prosthesis with respect to thebifurcation may be important. To facilitate positioning of thetransition zone relative to the carina or other anatomical feature ofthe bifurcation, the prosthesis is preferably provided with a firstradiopaque marker at a distal end of the transition zone and a secondradiopaque marker at the proximal end of the transition zone. Theproximal and distal radiopaque markers may take the form of radiopaquebands of material, or discreet markers which are attached to theprosthesis structure. This will enable centering of the transition zoneon a desired anatomical target, relative to the ostium of thebifurcation. In general, it is desirable to avoid positioning the stentor other support such that it extends into the main vessel. A singlemarker may be used to denote the placement location of the transitionzone.

Alternatively, the marker band or bands or other markers may be carriedby the deployment catheter beneath the prosthesis, and axially alignedwith, for example, the proximal and distal ends of the transition zonein addition to markers delineating the proximal and distal end of theprosthesis.

Although the prosthesis has been disclosed herein primarily in thecontext of a distal branch vessel stent carrying a plurality ofproximally extending fronds, other configurations may be constructedwithin the scope of the present invention. For example, the orientationsmay be reversed such that the fronds extend in a distal direction fromthe support structure. Alternatively, a support structure such as astent may be provided at each of the proximal and distal ends of aplurality of frond like connectors. This structure may be deployed, forexample, with a distal stent in the branch lumen, a plurality ofconnectors extending across the ostium into the main vessel, and theproximal stent deployed in the main vessel proximal to the ostium. Aseparate main vessel stent may thereafter be positioned through theproximal stent of the prosthesis, across the ostium and into the mainvessel on the distal side of the bifurcation.

In addition, the prosthesis has been primarily described herein as aunitary structure, such as might be produced by laser cutting theprosthesis from a tubular stock. Alternatively, the prosthesis may beconstructed such as by welding, brazing, or other attachment techniquesto secure a plurality of fronds onto a separately constructed support.This permits the use of dissimilar materials, having a variety of hybridcharacteristics, such as a self expandable plurality of fronds connectedto a balloon expandable support. Once released from a restraint on thedeployment catheter, self expandable fronds will tend to bias radiallyoutwardly against the vascular wall, which may be desirable during theprocess of implanting the main vessel stent. Alternatively, the entirestructure can be self expandable or balloon expandable, or the supportcan be self expandable as is described elsewhere herein. In general, theproximal end of the fronds will contribute no incremental radial forceto the prosthesis. The distal end of the fronds may contribute radialforce only to the extent that it is transmitted down the frond from thesupport structure.

In each of the embodiments illustrated in FIGS. 2A-2E, the fronds havebeen illustrated as extending between a first end which is attached tothe support 52, and a second, free end. In any of the frond designsdisclosed herein, it may be desirable to provide a connection betweenthe fronds in the vicinity of the free end. The connection may beaccomplished in any of a variety of ways, such as providing a series ofinterfrond segments or connections, which, when deployed and expanded,form a circumferential ring which links the fronds. Alternatively, thecircumferential link may be frangible, such that it maintains thespatial orientation of the fronds prior to a final expansion step, butis severed or otherwise releases the fronds upon final expansion.

The provision of a circumferential link at the proximal end of thefronds may provide a variety of benefits. For example, in an embodimentintended for balloon expansion at the treatment site, thecircumferential link will assist in maintaining the crimped profile ofthe fronds on the balloon during transluminal navigation. Thecircumferential link may be configured with sufficient holding forcethat an outer sleeve such as those discussed in connection with FIGS. 5and 6 may be omitted. In addition, the provision of a circumferentiallink may provide sufficient radiopacity either by itself or by carryingseparate radiopaque markers to permit visualization of the ends of thefronds.

Once at the treatment site, the circumferential link will assist inmaintaining the spacing of the fronds and also in holding the proximalends of the fronds open to facilitate advancement of the main vesselstent therethrough. The circumferential link may additionally assist incontrolling the fronds if, during the procedure, it is determined tocrush the fronds against a wall of the vessel. The circumferential linkwill assist in maintaining the fronds against the wall while a secondarystrategy is employed.

The circumferential link may be provided by any of a variety oftechniques which will be understood to those in the stent manufacturingarts. For example, the circumferential link may be formed integrallywith the stent and fronds such as by laser cutting from tube stock.Alternatively, the circumferential link may be attached to previouslyformed fronds, using any of a variety of bonding techniques such aswelding, brazing, adhesives or others depending upon the materials ofthe fronds and circumferential link. Although it may add to the wallthickness, the circumferential link may be interlocked with or crimpedto the fronds.

The circumferential link may alternatively be a polymeric band ortubular sleeve. For example, a radially expandable tubular sleeve may bepositioned around the outside surface of the fronds, or adjacent thelumenal surface of the fronds. A polymeric circumferential link may alsobe formed such as by dipping the fronds or spraying the fronds with asuitable polymeric precursor or molten material. Polymericcircumferential links may be permanent, severable, or may bebioabsorbable or bioerodeable over time.

One embodiment of a circumferential link is illustrated schematically inFIG. 2F. In this embodiment, a circumferential link 120 is provided,which connects each adjacent pair of fronds together, to produce acircumferential link 120 which extends completely around the axis of theprosthesis. In this illustration, the circumferential link 120 thuscomprises a discrete transverse connection between each adjacent pair offronds. Thus, for example, a first segment 122 is provided between afirst and a second frond. The first segment 122 is expandable orenlargeable in a circumferential direction. A first segment 122 has afirst end 126 at the point of attachment of the first segment 122 to afirst frond, and a second end 128 at a point of attachment between thefirst segment 122 and a second frond. The arc distance or the lineardistance between the first end 126 and second end 128 measured in aplane transverse to the longitudinal axis of the prosthesis isenlargeable from a first distance for transluminal navigation, to asecond distance following expansion of the fronds within the mainvessel. To accommodate the radial expansion of the circumferential link120, the first segment 122 is provided with an undulating configurationhaving at least one and optionally 2 or three or more apex 130, as willbe understood in the art. In one embodiment, each adjacent pair offronds is connected by a transverse segment (e.g., 122, 124 etc.) andeach of the transverse segments is identical to each other transversesegments.

Although the first segment 122 and second segment 124 are eachillustrated in FIG. 2F as comprising only a single transverselyextending filament, two or three or more filaments may be providedbetween each adjacent pair of fronds, depending upon the desiredperformance. As used herein, the term “circumferential link” does notlimit the link 120 to only a single filament between adjacent fronds.For example, the circumferential link may comprise a stent or othersupport structure which is similar to the support structure 52.

Referring to FIG. 2G, there is illustrated a prosthesis in accordancewith the present invention illustrating a spiral frond configuration. Ingeneral, the prosthesis 50 comprises a support section 52 and a frondsection 54 generally as has been discussed previously. Depending uponthe desired performance characteristics, a transition section 60 may beprovided between the support section 52 and the frond section 54. In theillustrated embodiment, the proximal end of the frond section 54 isprovided with a circumferential link 120 as has been discussed.

The frond section 54 comprises a single frond 16, in the illustratedembodiment in the form of a single wire or filament, which extends in aspiral configuration about the longitudinal axis of the prosthesis. Thefrond 16 may comprise a single filament as illustrated, or may comprisea more complex, fenestrated or multi-filament configuration as has beendiscussed herein.

The frond 16 is additionally formed into a sinusoidal configuration,alternately having concavities facing in a proximal direction andconcavities facing distally. In the illustrated embodiment, the frond 16is provided with a sinusoidal pattern having a plurality of generallyoppositely facing substantially constant radius curves. The fronds 16may alternatively comprise a plurality of “U” shaped or “V” shapedundulations, or other configuration depending upon the desired clinicalperformance.

In the illustrated embodiment, a single frond 16 extends in a spiralabout the longitudinal axis of the prosthesis 50. Alternatively, twofronds 16 or three fronds 16 or more may be utilized, each spiralingabout the longitudinal axis, as will be apparent to those of skill inthe art in view of the disclosure herein.

The spiral frond 16 will generally extend for at least two completerevolutions about the longitudinal axis of the prosthesis. The frond 16will often extend through at least about 4 complete revolutions, and, insome embodiments, at least about 6 complete revolutions about thelongitudinal axis of the prosthesis. The axial length of the frondsection 54 in a helical frond embodiment will often be at least about25% of the overall, unstretched length of the prosthesis. In certainembodiments, the axial length of the frond section 54 will be at leastabout 30% of the overall unstretched length of the prosthesis.

At the distal end of the frond section 54, a connection is made to thesupport section 52. In the illustrated embodiment, a plurality ofconnectors 61 is provided. Connectors 61 may conveniently be formedintegrally with or attached to the support section 52 at any of avariety of locations, such as on one or more apexes 63. The connectors61 extend from the apex 63 to the frond 16, such as on a distally convexcurve or a distally concave curve of the frond 16. One or two or threeor four or more connectors 61 may be utilized to connect the frond 16 tothe support section 52. In the illustrated embodiment, each apex 63 onthe proximal end of the support section 52 is provided with a uniqueconnector 61, for connection to the frond 16. As can be appreciated bythose of skill in the art, the axial length of the connectors 61 willenlarge progressively at progressive circumferential positions about theaxis of the support section 52, to accommodate the inclined angle of thedistal most loop of frond 16, which, due to its spiral configuration,resides on a transverse plane which is inclined at an angle θ withrespect to the longitudinal axis of the prosthesis 50. In spiral frondembodiments, the angle θ can be within the range of from about 95° toabout 170°. In spiral frond embodiments, the angle θ can be within therange of from about 95° to about 135°. In spiral frond embodiments, theangle θ can be about 110°.

In the embodiment illustrated in FIG. 2G, the proximal end of the frond16 is provided with a circumferential link 120. Circumferential link 120may be connected to the frond 16 in a variety of ways, such as byproviding one or more connectors 121. Connector 121 is illustrated asconnected to or formed with an apex 123 on the sinusoidal frond 16, andalso to a distally facing apex 125 on the circumferential link 120. Asecond connector 128 is illustrated, similarly connected between aproximally facing convexity on the frond 16 and a distally facingconvexity on the circumferential link 120. In the illustratedembodiment, every other apex 125 on the circumferential link 120 isprovided with a connector for connection to the frond 16. Alternatively,every third apex 125 or every apex 125 may be connected to the frond 16by a connector 121.

In many ways the prosthesis illustrated in FIG. 2G may be utilized in amanner similar to other prostheses disclosed herein. However, the spiralconfiguration of fronds 16 provides a greater level of radial supportthan many of the other frond configurations disclosed herein. As aconsequence, the spiral frond configuration may also be utilized as aprovisional side branch stent while other configurations may lacksufficient radial force to be used in this manner. In a provisionalstenting, the stent is placed in the side branch and then evaluated forwhether a second stent is desirable. The spiral wound frond exhibitssufficient radial force that it may be used either alone or with asecond stent. If a second stent is desired, it may be advanced throughthe side wall of the spiral frond 16 and into the main vessel as hasbeen discussed. Alternatively, the spiral frond prosthesis may be leftas a single stent, depending upon the desired clinical performance.

In addition, the spiral fronds support the cantilevered transition zone60 such that radial strength is provided within the ostium of thebifurcation.

FIGS. 2H-2I shows other embodiment of prostheses 400, 440 (in “rolledout” patterns) that include support or stent sections having a closedcell structure. The prostheses 400, 440 have frond sections that havebeen modified to enhance to performance and interaction thereof with amain vessel stent to be deployed therewith. The prostheses 400, 440 maybe configured in some respects similar to those described hereinabove.

The prosthesis 400 is adapted for placement at an ostium opening from amain body lumen to a branch body lumen and, as shown in FIG. 2H,includes a stent section 402, transition section 404, and a frondsection 406. The stent section 402 is generally tubular and is disposedon a distal portion of the prosthesis.

The stent section 402 comprises a distal end of 408, a proximal and 410,and a wall surface 412 extending therebetween. The wall surface 412 isformed of a plurality of circumferentially arranged undulating members414, 416, 418. In one construction, each trough of the undulating number414 is fixedly coupled with a corresponding crest of the undulatingnumber 416. In one construction each trough of the undulating number 416is fixedly coupled with corresponding crest of the undulating member418. Although additional undulating members can be provided between theundulating number 416 and the proximal end 410 of the stent section 402,in one embodiment the undulating number 418 is coupled with thetransition section 404 of the prosthesis 400. In one arrangement, theundulating number 418 includes alternating shallow and deep troughs420A, 420B that are coupled with a distal portion of the transitionsection 404, as discussed below. The deep and shallow trough's 420A,420B comprise proximal apices of the stent section 402.

Adjacent undulating members 414, 416 define closed cells 422therebetween. The closed cells 422 are defined between distal andproximal apices. The distal apices correspond to crest of the undulatingnumber 414. The proximal apices correspond to troughs of the undulatingnumber 416. When expanded, lateral aspects of the closed cells 422 moveapart circumferentially, such that a greater distance is defined betweenthe central portion of the lateral members forming the circumferentialsides of the cells 422. This movement produces expansion of the cellsand also moves apart adjacent troughs of the undulate number 414 andadjacent crests of undulating number 416. The crests and troughs aredirectly coupled with one another in the embodiment of FIG. 2H. In theexpanded state, the wall surface 412 comprises a plurality ofsubstantially diamond shaped cells 422.

The stent section 402 provides a radially expansible support that isconfigured to be deployed in at least a portion of the branch body lumenas part of a treatment to maintain flow through the branch body lumen.

The transition section 404 can take any suitable form, but preferably isconfigured to support the carina or ostium at the bifurcation whendeployed. The transition section 404 is similar to those hereinbeforedescribed, e.g., in connection with FIGS. 2D-2F. In one embodiment thetransition section 404 includes alternating filament sections 424, 426.The filament sections 424 are generally thinner than the filamentsections 426. The filament sections 424 are configured to extenddistally farther than the filament sections 426 in one embodiment. Thefilament sections 424 can be couple with the shallow troughs 420A andthe filament sections 426 can be couple with the deep troughs 420B ofthe undulating number 418 in one embodiment. By configuring theundulating member 418 with shallow and deep troughs 420A, 420B, agreater amount of material can be incorporated into the transitionsection 404. This is because the filaments coupled with the shallowtroughs 402A can be lengthened compared to an embodiment where all ofthe proximal apices extend to a same axial location corresponding to thelocation of the deep troughs 402B. By providing a greater amount ofmaterial, the transition section 404 is able to provide a greater degreeof scaffolding in the area of the ostium. This enhances the ability ofthe prosthesis 400 to effectively maintain the ostium open afterimplantation.

In one embodiment, the transition section 404 has a distal section withfour side-by-side filaments. In one embodiment, the distal section ofthe transition section 404 includes two filaments of the relatively thinfilament sections 424 and two filaments of relatively thicker filamentssections 426 located on opposite sides of the filament section 424. Thetransition section 404 can be configured with a proximal section havingonly two side-by-side filaments 429. The two side-by-side filaments 429can take any suitable form, but preferably comprise an undulatingpattern. For example, the two side-by-side filaments 429 can comprise agenerally sinusoidal pattern wherein the filaments are in-phase. In oneembodiment, the transition portion 404 includes a dual serpentinesection as shown in FIG. 2H.

The transition section 404 can be configured to optimally scaffold theanatomy at a bifurcation. For example, the proximal portion of thetransition section 404 can be configured to provide sufficient supportat the bifurcation for a treatment. In some applications using a second,main vessel stent deployed in conjunction with the prosthesis 400, atleast a portion of the bifurcation may be supported primarily (or only)by the transition portion. Therefore, it may be desirable to increasethe amount of material or stiffness of the material at the transitionportion. In some embodiments, this can be achieved by maximizing theamount of coverage at the bifurcation. Also, optimal coverage of thecarina may depend upon the geometry of the bifurcation. Where the angleof the branch vessel to the main vessel is high (e.g., approaching 90°),a shorter transition portion is suitable. However, when the angle of thebranch vessel to the main vessel is low (e.g., 45° or less), a longertransition portion is beneficial to provide sufficient coverage at thebifurcation. A shorter transition portion is described below inconnection with FIG. 2L.

The frond section 406 includes a plurality of fronds 432 that extendaxially proximally of the proximal end 410 of the stent section 402. Thefronds 432 extend between the transition section 404 and a proximal end430 of the prosthesis in one embodiment. In the expanded state, thefronds 432 define lateral (circumferential) boundaries of windows 433through which a main vessel stent can be deployed, as discussed herein.In one arrangement, each of the fronds 432 comprises a single filamentthat extends from the proximal section of the transition section 404 toa proximal end 434 of the fronds 432. The fronds 432 are configured tobe deformably deployed in at least a portion of the main body lumen andto apply less radial force to adjacent tissue than the expanded supportapplies in the branch body lumen.

The length of the fronds 432 can be selected based on a number offactors. In some embodiments, the length of the fronds is a function ofthe size of the vessel into which the prostheses described herein are tobe deployed. For example, if the prosthesis 400 is to be deployed in asmall vessel and if the main vessel at which the bifurcation is formedis also small, than the windows between the fronds will be relativelysmall, even in the expanded state. As a result, there is a greater needfor a high degree of alignment of the main vessel stent with the window433 formed in the branch vessel stent. By providing longer windows,there can be greater assurance of proper alignment through the windows433.

In the embodiment of FIG. 2H, a circumferential link 436 is providedthat has an undulating configuration comprising a plurality of apices.The circumferential link 436 connects each of the proximal ends 434 ofthe fronds 432. The proximal end 434 of each frond 432 is connected to adistal apex of the circumferential link. The circumferential link 436forms a proximal boundary of the windows 433 in one embodiment.

In one embodiment, some of the apices of the circumferential link arenot connected from adjacent fronds 432. For example, in one embodiment,every other apex of the circumferential link 436 is not connected to afrond. Providing a greater number of unconnected apices on thecircumferential link enables a greater amount of expansion of thecircumferential link 436 while maintaining a relatively short axial zonein which the circumferential link 436 is located in the unexpandedstate.

FIG. 2I shows that that the prosthesis 440 has a stent section 442 thatis configured as a closed cell structure, in which a plurality of cells444 are provided. As used herein, a closed cell structure is one inwhich all or substantially all of the peaks and troughs of a cell areconnected to longitudinally adjacent cells.

Each of the cells 444 comprises a distal apex 446, a proximal apex 448,a first lateral deformable section 450, and a second lateral deformablesection 452. In the embodiment of FIG. 2I, the distal and proximalapices 446, 448 correspond to crests and troughs of adjacent sinusoidalmembers 454, 456. The sinusoidal members 454, 456 extendcircumferentially around the stent 440 in a formed (e.g., a tubular)configuration and are spaced apart along the length of the prosthesis440 by the deformable sections 450, 452. The deformable sections 450,452 can take any suitable form, but preferably are more flexible thanthe sinusoidal members 454, 456 such that the sections 450, 452 candeform upon application of a bending load (e.g., applied at the ends ofstent section 442). This arrangement increases the flexibility of thestent section 442 for delivery and conformance to tortuous vasculature.The sections 450, 452 also enable the stent to lengthen somewhat suchthat adjacent sinusoidal members 454, 456 can move closer to each otheror farther apart to accommodate curvature of the anatomy, for example.

In the illustrated embodiment, a distal end 460 of the deformablesection 450 connects to a trough 462 of a distal sinusoidal member 454and a proximal end 464 of the deformable section 450 connects to a crest466 of a proximal sinusoidal member 456. Across the cell 444, a distalend of the deformable section 452 connects to a trough of the distalsinusoidal member 454 and a proximal end of the deformable section 452connects to a crest of the proximal sinusoidal member 456. In oneembodiment, each of the distal ends of the deformable sections 450, 452is coupled with corresponding troughs of the sinusoidal member 454 at alocation latterly offset from the center of the troughs. In oneembodiment, each of the proximal ends of the deformable sections 450,452 is coupled with corresponding crest of the sinusoidal member 456 ata location latterly offset from the center of the crests. In oneembodiment, the crests and troughs of adjacent sinusoidal members 454,456 are circumferentially aligned, and the deformable sections 450, 452are connected on opposite sides of the centerline C_(L) of the alignedcrests and troughs 462, 466.

The deformable sections 450, 452 can take any suitable form. Forexample, the deformable sections 450, 452 can be generally N-shaped.Various embodiments, the deformable sections 450, 452 can comprise atleast one, e.g., two, generally circumferentially oriented undulations.The generally circumferentially oriented undulations are configured tobecome at least partially straightened during expansion of the stentsection 442 such that the adjacent sinusoidal members 454, 456 can havea different separation distance therebetween in an expanded statecompared to a non-expanded state. Also, the undulations permitcorresponding side of the adjacent sinusoidal members 454, 456 to movetoward each other while opposite corresponding side of the adjacentsinusoidal members 472, 456 move away from each other. This feature canenable the stent section 442 to flexibly obtain an appropriate shapeupon expansion based upon the anatomy of the patient.

The prosthesis 440 has a transition section 470 that can be similar tothose hereinbefore described. In the embodiment of FIG. 2I, a pluralityof filaments is provided that are coupled with a proximal mostsinusoidal member 472. The sinusoidal member 472 can be similar to thesinusoidal members 454, 456 or it can be modified to couple with thefilaments in the transition section 470. In one modification, thesinusoidal member 472 comprises alternating deep troughs 474 and shallowtroughs 476. In one embodiment, every other trough is a deep trough 474and every other trough is in shallow trough 476. In one embodiment aplurality of fronds 478 extend proximally within the transition section470 from the proximal most sinusoidal member 472. The transition section470 is otherwise similar to those hereinbefore described.

In one embodiment, each of the fronds 478 has a greater number offilaments within the transition zone 470 than it does proximal thereof.For example, the construction of the transition zone 470 and the fronds476 can be similar to that of FIG. 2H. In one embodiment, it may bedesirable to interconnect adjacent dual serpentine portion of thetransition portion distal of the fronds 478. For example one or moreconnectors 480 can be provided between parallel undulating filaments orfilamentous portions of a frond 478. In one arrangement the connector480 prevents the frond 478 for being overly floppy and prone toundesirable deformation.

FIGS. 2J and 2K illustrate various embodiments of prostheses in which anopen cell configuration is provided in a stent section. In one aspectand open cell configuration provides a plurality of undulating membersthat are circumferentially oriented and space apart along the length ofthe prosthesis. In the open cell configuration at least some of thepeaks of the undulating members are not directly connected to otherundulating members.

FIG. 2J illustrates a first in a prosthesis 500 with an open cellconfiguration that is adapted for placement at an ostium opening from amain body lumen to a branch body lumen and. The prosthesis 500 includesa stent section 502, a transition section 504, and a frond section 506.The stent section 502 is generally tubular when formed and is disposedon a distal portion of the prosthesis 500.

The stent section 502 comprises a distal end 508, a proximal end 510,and a wall surface 512 extending therebetween. The wall surface 512 isformed of a plurality of circumferentially arranged undulating members514, 516, 518, 520, 521. In one construction, the undulating number 514is only periodically connected with the adjacent undulating member 516by a connector 522. For example, the undulating number 514 can include arepeating pattern of two unconnected proximally oriented troughs 524followed by a connected peak 526.

They connected peak 526 of the undulating member 514 can be connected toa peak of to the adjacent undulating number 516 by the connector 522. Inone embodiment the connected peak 526 forms a proximally-facing bightwithin which the connector 522 extends. The distal end 530 of theconnector 522 connects to the inside portion of the bight. A proximalend 532 of the connector 522 connects with a peak of the adjacentundulating number 516. The connector 522 can take any suitable form, butpreferably includes at least one circumferentially oriented undulation534 that permits relative axial movement of the undulating members 514,516. The connector 522 enables the stent section 502 to elongate betweenone or more of the circumferentially arranged undulating members 514,516, 518, 520, 521.

Undulating members 516, 518, 520 are disposed internally within thestructure of this stent section 502. These undulating members 516, 518,520 are within the structure in that they are not located at theproximal or distal end of the stent section 502. In other embodiments,there can be more internally disposed undulating members or thesemembers can be eliminated entirely. The internally disposed undulatingmembers 516, 518, 520 are coupled with adjacent undulating members alongtheir distal ends at internal bight locations, as describe above, andalso at external peak locations. For example, a connector 522 connectsthe undulating members 518, 520 from a location within a proximallyfacing bight of the undulating member 518 to a distal aspect 519 of apeak of the undulating member 520.

FIG. 2J shows that two proximal peaks of the undulating member 518 aredisposed between the connector 522 and an adjacent connector 522 andthat these proximal peaks are not connected to distal aspects of theundulating member 520. These unconnected peaks provide flexibility suchthat the stent can be delivered more easily and can better conform tothe vasculature, compared to a closed cell structure. A distal peak ofthe undulating member 518 is connected by a connector 522 to aproximally oriented bight of the undulating member 516.

The undulating member 521 is located at the proximal end of the stentsection 502. The undulating number 521 is coupled with the adjacentundulating number 520 along the distal portion of the undulating number521 at every other peak (as is true of all undulating members except thedistal-most in this embodiment). In particular, connectors 522 extenddistally from distal peaks 536 of the undulating member 521. FIG. 2Jshows that in some embodiments, the proximal end 510 of the stentsection 502 includes distal peaks which are free of connection toadjacent structures. In particular, the peaks 526′ are disposed betweenthe distal peaks 536 and have proximally facing bights that are freefrom connectors.

The transition section 504 connects to the stent section 502 in a mannersimilar to those hereinbefore described. Each proximally oriented peak538 of the undulating member 521 is coupled with a filament section.Filament section 540 comprises two relatively thin filaments that extenddistally to and connect with every other peak of the undulating number521. Filament section 542 comprises relatively thick filaments thatextend distally to a location that is proximal of a location where thefilament section 542 couples with the stent section 502. In oneembodiment a generally axially oriented connector 544 extends betweenthe proximal end of every other peak 538 of the undulating number 521and the distal-most aspect of the filament section 542.

The transition section 504 and the frond section 506 are similar tothose described in connection with FIG. 2H. The frond section 506 caninclude a plurality of serpentine shaped fronds that are coupled with acircumferential link. These fronds form windows, as discussed above, fordelivery of a main vessel stent in some techniques.

FIG. 2K illustrates another embodiment of a prosthesis 580 that issimilar to the prosthesis 500. The prosthesis 580 includes a stentsection 582, a transition section 584, and a frond section 586. Thestent section 582 comprises a distal end 588, proximal end 590, and awall surface 592 extending therebetween.

The wall surface 592 includes a plurality of adjacent circumferentialbands 594 that share one or more members 596 in common. One or morepeaks 598 of one circumferential band 594 are longer than the otherpeaks 600. In some embodiments, one or more troughs 602 of the adjacentcircumferential band 594 are longer than the remaining troughs 604. Inone embodiment, both the peaks 598 and the troughs 602 are longer thanthe peaks 600 and troughs 604. The longer peaks 598 intersect with thelonger troughs 602 in one embodiment and share a member 596 in commonforming an X-shaped structure 608.

The resulting X-shaped structure 608 in the embodiment of FIG. 2K canhave one or more orientations in various embodiments. For example, in adistal-most circumferential band, the X-shaped structure 608 can beinclined toward in a first circumferential direction such that a distalportion of the X-shaped structure 608 is to the right of a distalprojection of the proximal portion of the X-shaped structure. In oneembodiment, the second-most distal circumferential band has an X-shapedstructure 608′ that is inclined in a second circumferential directionopposite of the first circumferential direction such that a distalportion of the X-shaped structure 608′ is to the left of a distalprojection of the proximal portion of the X-shaped structure. In oneembodiment, every other circumferential band has X-shaped portions thatare inclined in opposite directions. In one embodiment, eachcircumferential band has an X-shaped portion that is a mirror image ofthe X-shaped portions disposed on one or more immediately adjacentbands.

In the embodiment of FIG. 2K, there are three overlapping regions 610between adjacent circumferential bands 594. The distal end of each cell612 comprises two peaks 600 and two troughs 604 and the proximal end ofeach cell 612 is defined by two peaks 600 and two troughs 604. There canbe fewer or more overlapping regions 610 between adjacentcircumferential bands 594. The X-shaped structures 608, 608′ extend inoblique directions relative to the longitudinal axis of the stentsection.

In one embodiment, the distal-most circumferential band 594 comprisesdistal peaks 600 and the proximal-most circumferential band 594comprises proximal troughs 604. The filament sections 614 compriserelatively thin filaments and filament sections 616 comprise relativelythick filaments. The transition section 584 is similar to that of FIGS.2H-2J except that the filament sections 614, 616 connect to alternatingtroughs of the proximal-most band 594 of the stent section 582 atsubstantially the same longitudinal position, e.g., at the proximal end590 of the stent section 582.

The frond section 586 can be similar to those hereinbefore described,e.g., including a serpentine member that is coupled with acircumferential link.

FIG. 2L illustrates a prosthesis 640 having a stent section 642, atransition section 644, and frond section 646. The stent section 642includes a distal end 648, a proximal end 650, and a wall pattern 652extending therebetween. The wall pattern 652 is similar to thatdiscussed above in connection with the stent section 402 of FIG. 2H andwill not be described further here. Additionally, any of the stentsections or wall patterns described elsewhere in this application can besubstituted for the stent section 642 in various embodiments.

The transition section 644 and frond section 646 are similar to thosediscussed above in connection with FIG. 2H. The transition section 644includes a pair of relatively thin members 654 coupled with a proximalportion of the stent section 642 alternating with a pair of relativelythick members 656. Each frond extends proximally from the stent section642. The prosthesis 640 transitions in the transition section 644 fromfour generally side-by-side filaments to two generally side-by-sidefilaments. The prosthesis 640 further transitions from two generallyside-by-side filaments to a plurality of single filament fronds, whichextend proximally to a circumferential link 658.

In one embodiment, the transition portion 644 comprises two generallyside-by-side filaments that are relatively short. For example, theproximal portion of the transition portion 644 having two generallyside-by-side filaments can be configured such that the two filamentsinclude only one circumferential undulation 660. The single filamentfronds are substantially longer than the side-by-side (e.g., dualserpentine) portion. In one embodiment the single filament fronds areabout three times as long as the side-by-side portion of the transitionportion 644.

Making the side-by-side (e.g., dual serpentine) portion relatively shortis beneficial for branch vessels that are at or approaching 90° from themain vessel. In comparison, in connection with FIG. 2H, the portion ofthe frond 432 comprising to side-by-side filaments is much longer. Inthis embodiment, the single filament portion is about the same length asthe portion of the frond comprising to side-by-side filaments. Asdiscussed above, the prosthesis of FIG. 2H is optimized for low take-offangle bifurcations.

FIG. 2M illustrates a prosthesis 680 that is a modification of theprosthesis of FIG. 2I. In embodiment of FIG. 2M, the members definingthe stent section 682 and the transition section 684 have been modifiedto include drug containing portions 686. In this embodiment, the membershave been formed in a substantially flattened configuration. The drugcontaining portions 686 can take any suitable form, such as beingwell-shaped such that a drug can be deposited therein.

Additionally, the transition section 684 has been modified compared tothat shown in FIG. 2I to include a plurality of substantially straightmembers 688 extending proximally from a proximal end of the stentsection 682. The substantially straight members 688 comprised drugcontaining portions 686. In one embodiment, the drug containing portions686 are formed by laser cutting depressions or through-holes in thestructure of the stent section 682 or the members 688. Also, thesubstantially straight members 688 can take any suitable form. In theillustrated embodiment, the members 688 are angled proximally towardeach other such that they can be joined by a short circumferentialextending member 690. Drug containing portions 686 can also be formed onthe circumferentially extending member 690.

A plurality of single undulating filament fronds 692 extends proximallyfrom the circumferentially extending members 690 a circumferential link694 located at the proximal end of the prosthesis 680. In anotherembodiment, the single filament fronds 692 are configured to be loadedwith a drug for any suitable drug treatment, e.g., by including drugcontaining portions 686.

In some treatment techniques, portions of the prosthesis 680 that aredeployed in the main vessel are configured not to have a drug elutingportion. For example, it may be advantageous to deploy the prosthesis680 with a main vessel stent that has a drug eluting portion and for themain vessel portion of the prosthesis not to have a drug elutingportion. This can minimize interactions between drugs on the main vesselstent and any drugs that may be provided on the stent section 682, forexample, to better control the treatment provided in the main and branchvessels.

In some embodiments, the single filament section 692 can be configuredto be loaded with a drug such that the drug can be eluted into a mainvessel or main passageway when the prosthesis 680 is deployed. In otherembodiments, the circumferential link 694 can be configured to be loadedwith a drug such that the drug can be eluted into a main vessel or mainpassageway when the prosthesis 680 is deployed. In other embodiments,the single filament section 692 and the circumferential link 694 can beconfigured to be loaded with a drug such that the drug can be elutedinto a main vessel or main passageway when the prosthesis 680 isdeployed. Any suitable technique can be used to load a drug in thesingle filament section 692 and/or in the circumferential link 694. Forexample, these portions can be provided with well-shaped portions asdiscussed above. Embodiments where the single filament section 692and/or the circumferential link 694 are coated can be used, for example,with a main vessel stent that is not drug eluting.

FIGS. 2N-2O show another embodiment of a wall pattern for a prosthesis700, in a “rolled-out” format. The prosthesis 700 includes a stentsection 704, a transition section 708, a frond section 712, and a linksystem 714. The prosthesis 700 has similar features to some of theembodiments set forth above, for example, incorporating a similartransition section and a similar frond section to those described above.For example, the prosthesis 700 is not limited to the particular patternof the stent section 704 illustrated in FIG. 2N-2O, but can have anyother pattern including any of the patterns described herein orconventional designs. The link system 714 is configured to enhance thesecurement of the prosthesis 700 to a deployment device, as discussed ingreater detail below.

The stent section 704 serves to hold open a vascular region, e.g., abranch vessel distal a bifurcation, after being deployed. The stentsection 704 can be formed from an elongated tubular member such thatundulating components of radially expandable cylindrical elements 716thereof can be relatively flat in transverse cross-section. As such,when the stent section 704 is expanded, the cylindrical elements 716 arepressed into the wall of a vessel and as a result do not interfere withthe blood flow through the vessel. The cylindrical elements 716 of stentsection 704, which are pressed into the wall of the vessel, may in somecases be covered with endothelial cell growth which may further minimizeblood flow interference.

Undulating portions of the cylindrical sections 716 provide secureengagement with an inner surface of the vessel to prevent stent movementwithin the vessel. Furthermore, the cylindrical elements 716 are closelyspaced at regular intervals to provide uniform support for the wall ofthe vessel. The stent section 704 thus is well adapted to hold in placesmall flaps or dissections in the wall of the vessel.

FIGS. 2N-2O illustrate that the stent portion 704 includesinterconnecting elements 720 disposed between adjacent cylindricalelements 716. The interconnecting elements 720 on both sides of acylindrical element 716 can be placed to enhance the flexibility for thestent portion 704. In the embodiment shown in FIGS. 2N-2O, the stentportion 704 has four interconnecting elements 720, with a single element720 being located between adjacent cylindrical elements 716. Theinterconnecting elements 720 are positioned to be more than one completeundulation apart. In one embodiment, the interconnecting elements 720are spaced apart by approximately 90 degrees about the circumference ofthe stent portion 704. The alternation of the interconnecting elements720 results in a stent that is longitudinally flexible in alldirections. Various configurations for the placement of interconnectingelements are possible, and several examples are illustratedschematically in U.S. Pat. No. 5,603,721, which is hereby incorporatedby reference herein in its entirety.

In various embodiments, the interconnecting elements 720 can be securedto the cylindrical elements 716 in any suitable manner. For example, theinterconnecting elements 720 can be coupled with the peaks or valleys ofthe cylindrical elements 716. The arrangement of the interconnectingelements can be used to tailor shortening of the stent during theexpansion thereof.

The properties of the stent portion 704 may also be varied by alterationof the undulating pattern of the cylindrical elements 716. FIGS. 2N-2Oillustrate an example stent structure in which the cylindrical elementsare in serpentine patterns but out of phase with adjacent cylindricalelements. The particular pattern and how many undulations per unit oflength around the circumference of the cylindrical element 716, or theamplitude of the undulations, are optimized for different aspects ofperformance, such as radial stiffness or other mechanical requirements,optimal scaffolding, or other characteristics.

The link system 714 is configured to provide a secure connection betweena proximal portion of the prosthesis 700 and a delivery device, whichcan be a balloon as described below in connection with FIGS. 28 and 29.The link system 714 preferably includes a frond engagement portion 744located adjacent to a proximal end 748 of the frond section 712 and acatheter securement portion 752. Preferably the link system 714 isconfigured to at least partially isolate the frond engagement portion744 from the catheter securement portion 752. For example, as discussedbelow in connection with FIGS. 28 and 29, the frond section 712 cantransmit a significant amount of torque to the link system 714 duringadvancement and deployment. The frond engagement portion 744 can absorbsuch a torque and prevent significant disruption of the cathetersecurement portion 752.

In one embodiment, the frond engagement portion 744 comprises anundulating circumferentially expandable structure 756. Thecircumferentially expandable structure 756 can be configured similar tothe circumferential links hereinbefore described. In one embodiment, thecircumferentially expandable structure 756 includes a plurality of peaksand valleys that are axially arranged, with alternating peaks beingcoupled with the proximal ends 748 of each frond section 712.

The catheter securement portion 752 can take any suitable form, butpreferably is a circumferentially extending structure 760. The cathetersecurement portion 752 can be configured to surround a space that can beoccupied by a portion of a catheter, such as a balloon or otherexpansion device that can be used to expand the prosthesis 700 from alow-profile state for delivery to an expanded state. FIGS. 2N-2Oillustrate that the catheter securement portion 752 can include acircumferentially expandable structure 760 that has an undulatingconfiguration. The circumferentially expandable structure 760 can have agenerally sinusoidal pattern that is out-of-phase with a generallysinusoidal pattern of the circumferentially expandable structure 760.

The link system 714 can include an axial coupling 764 disposed betweenthe frond engagement portion 744 and the catheter securement portion752. The axial coupling 764 can take any suitable form, but preferablyprovides sufficient connection between the frond engagement portion 744and the catheter securement portion 752 to resist premature expansion ofa proximal portion of the frond engagement portion 744 from a lowprofile configuration. The frond engagement portion 744 has sufficientflexibility to absorb torque from the frond section 712 while at thesame time isolating distal portions of the catheter securement portion752 from such torque. Thus, the link system 714 is well adapted toprevent fronds in the frond section 712 from divaricating from adelivery device, such as a balloon catheter.

In one embodiment, the axial coupling 764 includes at least one butpreferably a plurality of axially extending connectors. In theillustrated embodiment, each of the connectors connects a peak 768 ofthe catheter securement portion 752 with a valley 772 of the frondengagement portion 744. The coupling 764 can be a generally straightmember or can have one or more undulations that can be provided toenhance the mechanical isolation of the frond engagement portion 744 andthe catheter securement portion 752.

FIG. 2O illustrates the transition of various structures of theprosthesis 700 from a collapsed state corresponding to FIG. 2N to anexpanded state FIG. 2O. The frond section 712 includes a plurality ofside-by-side filaments 780 that extend proximally from the transitionsection 708. Preferably the side-by-side filaments 780 extend through aplurality of axially oriented undulations within a distal portion of thefrond section 712 to a central portion of the frond section 712. Fromthe low profile state of FIG. 2N to the expanded state of FIG. 2O, theside-by-side filaments 780 open up to a generally V-shapedconfiguration. For example, distal portions of the side-by-sidefilaments 780 become spaced apart by a greater amount in the expandedstate than in the unexpanded state. Also, the spacing of theside-by-side filaments 780 is altered upon expansion from beinggenerally constant between the transition section 708 and the centralportion of the frond section 712 to being distally increasing inexpanded states. FIG. 2O shows that the increase in spacing betweenadjacent filaments of the side-by-side filaments 780 need not becontinuously increasing along the entire length of the frond section712. A greater spacing can be provided at a forward location 784adjacent to the transition section 708 compared to a central portion 788of the frond section 712.

FIG. 2P illustrates another embodiment of a prosthesis 800 that ismodified to provide for improved trackability within vessels. Theprosthesis 800 is similar to those hereinbefore described, for examplehaving a stent section 804, a transition section 808, and a link system814 similar to those of FIG. 2N-2O. The prosthesis 800 has a frondsection 812 that is modified to minimize adverse interactions within thevasculature when the prosthesis 800 is moved therein.

The frond section 812 includes a distal portion 822 and a proximalportion 826. The distal portion 822 is similar to the distal portion ofthe frond section 712, including a plurality of side-by-side membersextending between the transition section 808 and a central portion 830of the frond section 812. The proximal portion 826 is configured toprovide a larger angle of approach to structures disposed withinvasculature to reduce the effect of impact therebetween. For example, inone embodiment, the proximal portion 826 includes a single filamentportion 834 that extends from the central portion 830 to the link system814. The single filament portion 834 can have an undulatingconfiguration in some embodiments. The undulations can be elongated toreduce the greatest angle of approach between distal facing edges 838 ofthe filament and vascular structures that may be located distal of theprostheses 800 as it is being advanced. For example, the single filamentportion 834 preferably is arranged to minimize an angle relative to alongitudinal axis of the prosthesis 800. In one embodiment, the singlefilament portion 834 preferably is arranged have an angle of approachthat does not exceed 45 degrees relative to a longitudinal axis of theprosthesis 800. In one embodiment, the single filament portion 834preferably is arranged have an angle of approach is less than about 35degrees relative to a longitudinal axis of the prosthesis 800. In oneembodiment, the single filament portion 834 preferably is arranged havean angle of approach is about 20 degrees or less. In one embodiment, thesingle filament portion 834 preferably is arranged have an angle ofapproach is less between about 5 degrees and about 20 degrees relativeto a longitudinal axis of the prosthesis 800. In one embodiment, thesingle filament portion 834 has a substantially straight configuration.

Any of the prosthesis described herein, including those described inconnection with FIGS. 2H-2P, can be configured as bioerodablestructures. In certain embodiments, bioerodable structures arestructures that are absorbed into the body and eventually disappear, butwhich maintain structural integrity during substantially the entire lifeof the structure. In other embodiments, any of the prosthesis describedherein, including those described in connection with FIGS. 2H-2P, can beconfigured as biodegradable structures. In certain embodiments,biodegradable structures are structures that are absorbed into the bodyand eventually disappear, but that also lose a substantial amount oftheir structural integrity more rapidly than a bioerodable structure. Ingeneral terms, the prosthesis 50 may be considered to be a tubularstructure which comprises a plurality of axially extending fronds havinga first radially expandable structure on a first end and a secondradially expandable structure on a second end. The first radiallyexpandable structure is a support structure 52 such as a stent, as hasbeen described for positioning within the branch vessel. The secondradially expandable structure comprises the circumferential link 120.

Typically, the circumferential link 120 will provide significantly lessradial force than the first support structure 52, in view of its primaryfunction to maintain the spacing and orientation of the fronds ratherthan providing support to the vessel wall. In a typical embodiment, thesupport structure 52 will have a first radial force, the circumferentiallink 120 will have a second, lesser radial force, and the fronds willcontribute nothing or essentially nothing to the radial force of thestructure. Alternatively, the circumferential link 120 may have a radialforce which is approximately equal to the radial force of the supportstructure 52, and possibly even in excess of the radial force of thesupport structure 52, depending upon the desired clinical performance.The fronds may exhibit a radial force, which may be due mostly orentirely to the adjacent stent or circumferential link.

In an implementation of the invention intended for use in the coronaryarteries, the stent portion may have a crush resistance or radialstrength on the order of at least about 10 psi or 12 psi, and, often atleast about 14 or 15 psi. The circumferential link may have a radialforce or crush resistance of no greater than about 90%, often no greaterthan about 50%, and in some embodiments no greater than about 25% of theradial force or crush resistance of the branch vessel stent. Thus, in aprosthesis having a stent with a crush resistance of at least about 14or 15 psi, the circumferential link might have a crush resistance ofless than about 4 or 3 psi. The crush resistance in the fronds may beless than about 2 psi or less than about 1 psi, depending upon thelength of the fronds, structure of the fronds, crush resistance of theadjacent structures, and other factors that may affect the cantileveredtransfer of radial force from the adjacent stent or circumferentiallink.

Radial strength or crush resistance as used herein, may be determined inpsi by constructing a radial strength test fixture. In general, theradial strength test fixture comprises a pressured chamber, adapted toallow the insertion of a flexible tube which can be sealed at each endto the walls of the chamber such that the exterior wall of the tubing isexposed to the pressure generated in the chamber while the central lumenof the tube is exposed to ambient atmospheric pressure. Any of a varietyof thin walled flexible tubing may be utilized, such as a thin walledlatex tubing, such that the inside diameter of the latex tubing may beapproximately 10% less than the nominal expanded diameter of the stent.The stent is expanded within the tubing, such as by inflating anassociated dilation balloon to its rated burst pressure or otherpressure sufficient to expand the stent to its intended implanteddiameter. The balloon may be deflated and the balloon catheterwithdrawn. The tubing is mounted in the pressure chamber as describedabove. Air or other inflation media may be pumped into the pressurechamber to slowly increase the pressure within the chamber (for exampleat a rate of about 1 psi per second). Once any portion of the centrallumen through the prosthesis has been reduced under pressure to lessthan or equal to 50% of its original lumen diameter, the pressure in thechamber is noted and considered to be the radial force or crushresistance of the prosthesis.

The second radially expandable structure (circumferential link) may alsohave a shorter axial length than the first radially expandable structure(stent). For example, in a coronary artery embodiment, the axial lengthof the stent may be at least 300% or 500% or more of the length of thecircumferential link.

The fronds will have a length in the axial direction between the support52 and the circumferential link 120 of generally in excess of about 2.5mm or 3 mm, and in certain embodiments in excess of about 5 mm. At leastsome or all of the fronds may have a length in excess of about 8 mm,and, in one implementation of the invention intended for the coronaryartery, the frond length is in the vicinity of about 9.4 mm.

The circumferential link may also have a smaller strut profile comparedto the strut profile in the support 52. For example, the cross sectionaldimensions of a strut in the support 52 and/or the fronds may be on theorder of about 0.003 inches by about 0.055 inches in an embodimentintended for coronary artery applications. In the same embodiment, thecross sectional dimensions through a strut in the circumferential linkmay be on the order of about 0.001 inches by about 0.003 inches.

The frond length may also be evaluated relative to the main lumendiameter. For example, in the coronary artery environment, diameters inthe range of from about 2 mm to about 5 mm are often encountered. Frondlengths of at least about equal to the main vessel diameter (e.g. atleast about 2 mm or 3 mm or 4 mm or greater) are contemplated. Frondslengths of as much as 2 times or 3 times or 4 times or more of thediameter of the associated main vessel are also contemplated.

Deployment of the bifurcation prosthesis with linked fronds may beunderstood by reference to FIGS. 14A-14E. In FIG. 14A, the side branchguidewire 121′ has been positioned in the side branch and the mainvessel guidewire 123′ has been positioned in the main vessel. The sidebranch stent is next deployed in the side branch, with the frondsextending across the ostium and into the main vessel. Thecircumferential link 120 may either self expand or be balloon expandableto provide a main vessel stent opening. See FIG. 14B.

Referring to FIG. 14C, the side branch wire is retracted from the sidebranch and advanced between the fronds into the main vessel. The mainvessel wire 123 may be retracted at this point in the procedure. Themain vessel stent is then advanced over the wire through the openingformed by the circumferential link, and through a space between adjacentfronds into the desired position.

Referring to FIG. 14D, the main vessel stent is deployed to entrap thefronds against the vessel wall. The circumferential link is additionallytrapped against the vessel wall. Post dilation to open the side wallopening into the branch vessel may optionally be accomplished, byretracting the side branch wire and readvancing it into the side branch.See FIG. 14E.

In one embodiment, e.g., as shown in FIGS. 2Q, 2R, and 2S, theprosthesis 900 includes a radially expansible support 904 that can beimplanted as a stent. When implemented as a stent, the support 904 canhave any suitable wall pattern. For example, a wide variety of stentwall patterns are described herein in connection with FIGS. 2A-2F. Invarious embodiments, the support 904 includes a first end 908, a secondend 912, and an elongate body 916 therebetween. Many wall patterns thatcould be used in the prosthesis 900 would also include a plurality ofapices, which may be located throughout the length of the elongate body916, for example at the second end 912. Examples of such patterns areshown in FIGS. 2Q, 2S, and 2R, discussed further below.

In the context of a vascular bifurcation, a proximal region to thebifurcation is sometimes referred to as the proximal main vesselsegment, or sometimes “proximal main” herein. In the context of avascular bifurcation, there may be two or more lumens or vessels distalto the bifurcation. In some anatomy, a smaller vessel diverging at thebifurcation is referred to as a branch vessel or distal branch vesseland a continuation of the main vessel is referred to as the distal mainvessel, or sometime herein “distal main.”

In many treatments, it is desirable to treat the complex anatomy thatspans between the proximal main and one or more of the distal vessels.In some embodiments, the prosthesis 900 includes a transition portion920 (and/or a frond portion) that may be located at the second end 912of the support 904. The transition portion 920 can be configured as adifferent wall pattern disposed proximally of the support 904 that isadapted to treat this complex geometry. For example, as suggested byFIGS. 14B-1 and 14B-2, the transition portion 920 can have a first end924 at or coupled with the second end 912 of the support 904, a secondend 928 spaced apart from the support 904. In some embodiments, thetransition portion 920 has a circumferential surface area that is highertoward the first end 924 and lower toward the second end 928. As aresult, the amount of coverage of the complex anatomy of between theproximal main and the distal branch or distal main is greatest near thesupport 904 and becomes less at locations farther from the support 904.

Additionally, the transition portion 920 has a length 932 between thefirst and second ends 924, 928 that is configured to span the ostium,which is the complex anatomy between the distal and proximal vesselsegments. As shown in FIG. 14B-2, the second ends 928 of the transitionportion 920 reach a location PM in the proximal main and a location DMin the distal main.

FIGS. 14B-1 and 14B-2 illustrate that in some embodiments it isadvantageous that the transition portion 920 have a plurality of secondends 928 that may open up in different directions to follow the openingof the ostium in all directions.

As disclosed herein in connection with FIGS. 2A-2F, the transitionportion 920 coupled with proximal apices on a support 904 can have a onesection with a first plurality of (e.g., four) side-by-side filamentsand a another section with a second lesser plurality (e.g., two) ofside-by-side filaments. This provides a transition in radial strength aswell as scaffolding from the first end 924 to the second end 928 of thetransition portion 920. Lesser scaffolding is needed toward the secondend 928 in certain applications because a second prosthesis is implantedover or adjacent to the second end 928.

In one embodiment, the second end 928 of the transition portion 920 maytransition to a low profile structure in the region of the second end928. The low profile structure is sometimes referred to herein as afrond.

In one embodiment, a single filament 940 is provided that has a firstend 944 coupled with the transition portion 920 and a second end 948coupled with a circumferential member 952.

In one embodiment, the circumferential member 952 is provided on theproximal end of the prosthesis 900. The circumferential member 952 canbe adapted to anchor the prosthesis 900 as discussed further below.

The single filament 940 can be configured in any suitable fashion thatconnects the circumferential member 952 to distal portions of theprosthesis 900. For example, the single filament 940 can be a serpentineor sinusoidal member or can otherwise be configured to elongate whendesired within the vessel.

In some embodiments, the single filament 940 is configured withsufficient column strength to act as a compression member within thevessel to control the position of one or more of the components of theprosthesis 900. For example, the single filament 940 can be a rigid barthat can prevent the support 904 from moving out of the distal branchvessel upon expansion. Some combinations of the configuration of thesupport 904 and the anatomy in which it is implanted cause a proximallydirected force to be applied to the transition portion 920 that issufficient to shift the support 904 proximally during the process ofexpansion. This can result in the support 904 moving proximally towardthe proximal main, for example. It is desirable to prevent this proximalmovement.

One way to prevent such proximal movement is to deploy the prosthesis900 such that the circumferential member 952 engages securely with theblood vessel. Once it has been engaged, the support 904 and transitionportion 920 can be expanded to cover the anatomy as depicted in FIG.14B-2. The single filament 940 acts as a compression member transferringany force being applied to the support 904 or transition portion 920 tothe circumferential member 952. As a result, the position of the supportand transition portion 904, 920 can be maintained during expansion tominimize or prevent dislocation of the distal portion of the prosthesis900 in use.

As discussed herein, the circumferential member 952 can also beadvantageously configured as a guidance device to position a secondprosthesis if desired. See, e.g., FIGS. 14A-14E, which are described indetail herein. The prosthesis 900 would replace the prosthesis 54 inthis technique, but would include a single filament 940 connecting thecircumferential member 952 with the support 904. One or more frondswould be unconnected to the circumferential member 952.

FIGS. 2Q, 2R, and 2S illustrate three embodiments of the prosthesis. InFIG. 2Q, the prosthesis is configured for deployment using a balloon orother mechanical expansion device that applies outward force from insidethe prosthesis to expand the prosthesis. In FIG. 2R, the prosthesis isconfigured to be at least partially self-expanding. For example, asupport and/or a transition and/or frond portion of the prosthesis ofFIG. 2R can be made to self-expand upon actuation (e.g., withdrawal of asheath) in the vessel. FIG. 2S shows an expanded embodiment of theprosthesis.

FIGS. 2Q, 2R, and 2S illustrate that in one embodiment, thecircumferential member 952 can be configured with two circumferentialrings coupled together with either an expandable axial link or astraight link.

In one variation not specifically depicted, more than one but not all ofa plurality of fronds could be linked with the circumferential member952. For example, two fronds could be linked to the circumferentialmember 952. This arrangement could advantageously assist in thevisualization of the orientation of the prosthesis 900.

In some techniques, it is beneficial to be able to direct at least aportion of the device to a specific position. For example, it may bedesirable to position any loose frond on the distal side of the ostiumsuch that advancement of a second device (as illustrated in connectionwith FIG. 14D) pushes the free end of the loose frond distally and awayfrom the ostium. This prevents or minimizes the chance for the loosefrond to jail a distal branch vessel.

In some combinations of configurations of the prosthesis 900 and theostium, there may be a tendency for the support 904 to slip too far intoa distal vessel, e.g., the distal branch vessel. In these situations, itmay be sufficient for the single filament 940 to be a tension member,e.g., a structure that is capable of resisting a tensile force of themagnitude applied during deployment of the prosthesis 900 or by theanatomy before, during or after deployment. Of course, the singlefilament 940 can be a tension and compression member if so desired.

In the figures and through this description, there has been discussionof a “single” filament member 940. It is also possible to modify theprosthesis 900 such to have a single member disposed between the support904 and the circumferential member 952, e.g., a single frond connectedto the circumferential member 952, that has more than one filament toanchor other devices that have one or more loose transition and frondsections. For example, a member with a dual serpentine member extendingtoward the support 904 from the circumferential member 952 could beprovided, as illustrated herein in FIG. 2H.

Based upon the foregoing description, it will be apparent to those ofskill in the art that the prosthesis of the present invention may beimplanted in a variety of alternative manners. For example, the firstsupport structure (described above as a side branch stent) may bepositioned in the main vessel, distally (from the perspective of thedelivery catheter) of the bifurcation with the fronds extendingproximally across the opening to the side branch. The second supportstructure (referred to above as a circumferential link), if present, ispositioned in the main vessel proximally of the side branch opening. Astandard stent may then be positioned such that the distal end of thestent is within the side branch, and a proximal end of the stent iswithin the main vessel, such as within the circumferential link.

Referring now to FIGS. 3A-8, in various embodiments prosthesis/deliverysystem 205 can include a prosthesis with stent 210 and fronds 220 whichare configured to be captured or otherwise radially constrained by thedelivery system during advancement of the stent through the vasculatureor other body lumen. As shown in FIGS. 3A-3B, fronds 220 can beseparated by axial gaps or splits 230 along the length of the frondstructure. Splits 230 can have a variety of widths and in variousembodiments, can have a width between 0.05 to 2 times the width of thefronds, with specific embodiments of no more than about 0.05, 0.25, 0.5,1 and 2 times the width of the fronds. Fronds 220 can be configured tohave sufficient flexibility to be advanced while in a captured modethrough curved and/or tortuous vessels to reach the more distal portionsof the vasculature such as distal portion of the coronary vasculature.This can be achieved through the selection of dimensions and/or materialproperties (e.g. flexural properties) of the fronds. For example, all ora portion of fronds 220 can comprise a resilient metal (e.g., stainlesssteel) or a superelastic material known in the art. Examples of suitablesuperelastic materials include various nickel titanium alloys known inthe art such as Nitinol™.

Any of a variety of modifications or features may be provided on thefronds, to enhance flexibility or rotatability in one or more planes.For example, fronds may be provided with a reduced thickness throughouttheir length, compared to the thickness of the corresponding stent. Thethickness of the frond may be tapered from relatively thicker at thedistal (attachment) end to the proximal free end. Fronds may be providedwith one or more grooves or recesses, or a plurality of wells orapertures, to affect flexibility. The specific configuration of any suchflexibility modifying characteristic can be optimized through routineexperimentation by those of skill in the art in view of the presentdisclosure, taking into account the desired clinical performance.

It is desirable to have the fronds captured and held against thedelivery catheter or otherwise restrained as the stent is advancedthrough the vasculature in order to prevent the fronds from divaricatingor separating from the prosthesis delivery system prosthesis. Capture ofthe fronds and prevention of divarication can be achieved through avariety of means. For example, in various embodiments the capture meanscan be configured to prevent divarication by imparting sufficient hoopstrength to the fronds, or a structure including the fronds, to preventthe fronds from separating and branching from the deployment balloon asthe balloon catheter is advanced through the vasculature includingtortuous vasculature. In theses embodiments, the capture means is alsoconfigured to allow the fronds to have sufficient flexibility to beadvanced through the vasculature as described above.

In an embodiment shown in FIGS. 3A-4B, the fronds can be captured underthe flaps 242 of a deployment balloon 241 of a delivery balloon catheter240. In this and related embodiments, the balloon 241 and stent 210 canbe configured such that flaps 242 are substantially matched up oraligned with splits 230. This can be achieved using alignment techniquesknown in the art (e.g., use of alignment fixtures) when the stent 220 ispositioned over balloon 241. The flap material will initially extend orprotruded through the splits, but is then folded over onto one or morefronds 220 to capture those fronds. In an embodiment, this can beachieved by partially inflated and then deflated the balloon, withfolding done after the inflation or deflation. Folding can be done byhand or using a capture tube or overlying sleeve known in the art. Alsoin an embodiment, folding can be facilitated by the use of one or morepreformed folds 243, also known as fold lines 243. Folds 243 can beformed using medical balloon fabrication methods known in the art suchas mold blowing methods known in the art. In an embodiment using folds243, folding can be achieved by inflating the balloon with the overlyingfronds in place, so as to have the balloon flaps 242 protrude throughsplits 230, then the balloon is deflated to have flaps 242 fold backover fronds 220 at fold lines 243.

Once stent 210 is properly positioned at the target vessel site, balloon241 is at least partially inflated which unfurls flaps 242 coveringfronds 220 so as to release the fronds. Once released, deploymentballoon 241 can also be used to expand or otherwise deform the fronds220 to deploy them in the selected vessel as is described herein.Alternatively, a second balloon can be used to expand and deploy thefronds as is also described herein.

To avoid pinching the balloon material of balloon 241 between layers ofstent metal during the stent crimping process in one embodiment, fronds220 can be configured such that they do not overlap when crimped down toa smaller diameter. This can be achieved by configuring the fronds to besufficiently narrow so that crimping the stent to a smaller diameterdoes not cause them to overlap, or through the use of a crimping fixtureor mandrel known in the art. In various embodiments, fronds 220 can beconfigured to have a selectable minimum split width 230 w between spits230 after crimping. This can be in the range of 0.001 to about 0.2inches with specific embodiments of 0.002, 0.005, 0.010, 0.025, 0.050 or0.1 inches.

In another embodiment for using the delivery balloon catheter to capturethe fronds, a section of a balloon 241 (not shown) can be configured toevert or fold back over a proximal portion of the stent and thus overlyand capture the fronds. When the balloon is inflated, the overlyingsection of balloon material unfolds, releasing the fronds. The evertedsection of balloon can over all or any selected portion of the fronds.Eversion can be facilitated through the use of preformed folds describedherein, in the case, the folds having a circumferential configuration.The folded section of balloon can be held in place by a friction fit orthrough the use of releasable low-strength heat bond or adhesive knownin the art for bonding the balloon to the fronds. In one embodiment forpositioning the everted section, the balloon is positioned inside thescaffold section of the stent and then partially inflated to have an endof the balloon protrude outside of the scaffold section, then theballoon is partially deflated and everted section is rolled over thefronds and then the balloon is fully deflated to create a vacuum orshrink fit of the balloon onto the fronds.

In various embodiments, fronds 210 can be captured by use of a tubularcuff 250 extending from the proximal end 241 p of delivery balloon 241as is shown in FIGS. 5A-5C. In one embodiment, the cuff is attached tothe catheter at or proximal to the proximal end 241 p of the deliveryballoon. In alternative embodiments, the cuff can be attached to a moreproximal section of the catheter shaft such that there is an exposedsection of catheter shaft between balloon and the cuff attachment pointwith the attachment point selected to facilitate catheter flexibility.Alternatively, the cuff is axially movably carried by the cathetershaft, such as by attachment to a pull wire which extends axially alongthe outside of or through a pull wire lumen within the catheter shaft,or to a tubular sleeve concentrically carried over the catheter shaft.In either approach, the cuff is positionable during translumenalnavigation such that it overlies at least a portion of the fronds 220.

After prosthesis 210 is positioned at the target vascular site, thestent region is deployed using the delivery balloon as described herein.The frond(s) can be released by withdrawal of the restraint. In mostembodiments, the entire catheter assembly including the cuff or otherrestraint, balloon, and catheter shaft are withdrawn proximally to fullyrelease the fronds. In alternative embodiment the cuff can be slidablywithdrawn while maintaining position of the delivery balloon. Thisembodiment permits frond release prior to or after stent deployment.

Release of the fronds by the cuff can be achieved through a variety ofmeans. In one embodiment, cuff 250 can be configured such that theproximal frond tips 220 t, slip out from the cuff when the balloon isdeployed. Alternatively, the cuff may be scored or perforated such thatit breaks at least partially open upon balloon deployment so that itreleases fronds 220. Accordingly, in such embodiments, cuff 250 can haveone or more scored or perforated sections 250 p. In such embodiments,portions of cuff 250 can be configured to break open at a selectableinflation pressure or at a selectable expanded diameter. In oneembodiment, the cuff material can be fabricated from a polymer that itis more plastically deformable in a radial direction than axially. Suchproperties can be achieved by extrusion methods known in the polymerarts so as to stretch the material axially. In use, such materials allowthe cuff to plastically deform in the radial when expanded by thedeployment balloon, and then to stay at least partially deformed whenthe balloon is deflated so as to still cover the fronds. An example ofsuch a material includes extruded Low density Polyethylene (LDPE).Further description of the use of the cuff 250 and other capture meansmay be found in U.S. patent application Ser. No. 10/965,230 which isfully incorporated by reference herein.

In various embodiments, cuff 250 can be configured such that itplastically deforms when the balloon is inflated and substantiallyretains its “inflated shape” 250 is and “inflated diameter” 250 id afterthe balloon is deflated is shown in FIGS. 5B and 5C. This can beachieved through the selection of plastically deformable materials forcuff 250 (e.g. plastically deformable polymers), the design of the cuffitself (e.g. cuff dimensions and shape) and combinations thereof. Forexample, a cuff fixed to a catheter shaft and having the sameapproximate internal diameter as the deployed stent may be folded overthe stent fronds to constrain them (using conventional balloon foldingtechniques). That cuff may be unfolded when the stent deployment balloonis inflated and the fronds released. The cuff can be withdrawn along theballoon and catheter. In an alternative embodiment of a folded-overcuff, the cuff is relatively inelastic and has an internal diameterapproximately that of the deployed stent.

Also the cuff can be configured such that it shortens axially as it isexpanded by the deployment balloon or other expansion device. This canbe accomplished by selecting the materials for cuff 250 such that thecuff shrinks axially when it is stretched radially as is shown in FIGS.6A and 6B. Accordingly, in one embodiment, the cuff can be made ofelastomeric material configured to shrink axially when stretchedradially.

In another embodiment, all or a portion of the cuff can be configured tofold over or evert onto itself upon inflation of the balloon to producean everted section 251 and so release the enveloped fronds as is shownin FIGS. 6C-6D. This can be facilitated by use of fold lines 252described herein, as well as coupled the cuff to the balloon catheter.In one embodiment the cuff can be coaxially disposed over the proximalor distal end of the balloon catheter or even slightly in front ofeither end. This allows the cuff to disengage the fronds yet remainattached to the balloon catheter for easy removal from the vessel. Inuse, these and related embodiments allow the fronds to be held againstthe balloon to be radially constrained or captured during stentadvancement and then easily released before, during or after ballooninflation to deploy the stent at the target site.

In various embodiments, all or a portion of cuff 250 can be fabricatedfrom, silicones, polyurethanes (e.g., PEPAX) and other medicalelastomers known in the art; polyethylenes; fluoropolymers; polyolefin;as well as other medical polymers known in the art. Cuff 250 can also bemade of heat shrink tubing known in the art such as polyolefin and PTFEheat shrink tubing. These materials can be selected to produce a desiredamount of plastic deformation for a selected stress (e.g. hoop stressfrom the inflation of deployment balloon). In particular embodiments,all or a portion of the materials comprising cuff 250 can be selected tohave an elastic limit lower than forces exerted by inflation of thedeployment balloon (e.g., the force exerted by 3 mm diameter ballooninflated to 10 atms). Combinations of materials may be employed suchthat different portions of the cuff (e.g., the proximal and distalsections or the inner and outer surfaces) have differing mechanicalproperties including, but not limited to, durometer, stiffness andcoefficient of friction. For example, in one embodiment the distalportion of the cuff can high a higher durometer or stiffness than aproximal portion of the cuff. This can be achieved by constructing theproximal portion of the cuff from a first material (e.g., a firstelastomer) and the distal portion out of a second material (e.g. asecond elastomer). Embodiments of the cuff having a stiffer distalportion facilitate maintaining the fronds in a restrained state prior todeployment. In another embodiment, at least a portion of an interiorsurface of the cuff can include a lubricous material. Examples ofsuitable lubricious materials include fluoropolymers such as PTFE. In arelated embodiment, a portion of the interior of the cuff, e.g., adistal portion, can be lined with lubricous material such as afluoropolymer. Use of lubricous materials on the interior of the cuffaids in the fronds sliding out from under the cuff during balloonexpansion.

Referring now to FIGS. 7A-7B, in another embodiment for restraining thefronds, a tether 260 can be placed over all or portions of fronds 200 soas to tie the fronds together. Similar to the use of cuff 250, tether260 can be released by the expansion of the balloon 241. Accordingly,all or a portion of the tether can be configured to plastically deformupon inflation of balloon 241 so as to release the fronds.Alternatively, the tether can be configured to be detached from thefronds prior to expansion of the balloon. In one embodiment, this can beachieved via a pull wire, catheter or other pulling means coupled to thetether directly or indirectly.

In various embodiments, the tether can be a filament, cord, ribbon, etc.which would simply extend around the fronds to capture them like alasso. In one embodiment the tether can comprise a suture or suture-likematerial that is wrapped around the fronds. One or both ends of thesuture tether can be attachable to a balloon catheter 241. In anotherembodiment, tether 260 can comprise a band or sleeve that fits overfronds 220 and then expands with expansion of balloon 241. In this andrelated embodiments, tether 260 can also be attached to balloon catheter241. Also tether 260 can be scored or perforated so that a portion ofthe tether shears or otherwise breaks upon balloon inflation, therebyreleasing the fronds. Further, the tether 260 can contain a radio-opaqueother medical image visible marker 260 m to allow the physician tovisualize the position of the tether on the fronds, and/or determine ifthe tether is constraining the fronds.

Referring now to FIGS. 8A-8B, in other embodiments of the deliverysystem 10, the fronds can be constrained through the use of a removablesleeve 270 that can be cover all or a portion of fronds 220 duringpositioning of the stent at the target tissue site and then be removedprior to deployment of the fronds. In one embodiment, sleeve 270 can beslidably advanced and retracted over stent 210 including fronds 220.Accordingly, all or portions of sleeve 270 can be made from lubricousmaterials such as PTFE or silicone. Sleeve 270 can also include one ormore radio-opaque or other imaging markers 275 which can be positionedto allow the physician to determine to what extent the sleeve iscovering the fronds. In various embodiments, sleeve 270 can be movablycoupled to catheter 240 such that the sleeve slides over either theouter or inner surface (e.g., via an inner lumen) of catheter 240. Thesleeve can be moved through the use of a pull ire, hypotube, stiff shaftor other retraction means 280 known in the medical device arts. In oneembodiment, sleeve 270 can comprise a guiding catheter or overtube as isknown in the medical device arts.

Referring now to FIGS. 9A-11B, an exemplary deployment protocol forusing delivery system 5 to deliver a prosthesis (10) having a stentregion (12) and having one or more fronds (16) will be described. Theorder of acts in this protocol is exemplary and other orders and/or actsmay be used. A delivery balloon catheter 30 is advanced within thevasculature to carry prosthesis 10 having and stent region (12) andfronds 16 to an Os O located between a main vessel lumen MVL and abranch vessel lumen BVL in the vasculature, as shown in FIGS. 9A and 9B.Balloon catheter 30 may be introduced over a single guidewire GW whichpasses from the main vessel lumen MVL through the Os O into the branchvessel BVL. Optionally, a second guidewire (not shown) which passes bythe Os O in the main vessel lumen MVL may also be employed. Usually, theprosthesis 10 will include at least one radiopaque marker 20 onprosthesis 10 located near the transition region between the prosthesissection 12 and the fronds 16. In these embodiments, the radiopaquemarker 20 can be aligned with the Os O, typically under fluoroscopicimaging.

Preferably, at least one proximal marker will be provided on theprosthesis at a proximal end of the transition zone, and at least onedistal marker will be provided on the prosthesis at the distal end ofthe transition zone. Two or three or more markers may be provided withinthe transverse plane extending through each of the proximal and distalends of the transition zone. This facilitates fluoroscopic visualizationof the position of the transition zone with respect to the Os.Preferably, the transition zone is at least about 1 mm and may be atleast about 2 mm in axial length, to accommodate different clinicalskill levels and other procedural variations. Typically, the transitionzone will have an axial length of no more than about 4 mm or 5 mm (forcoronary artery applications).

During advancement, the fronds are radially constrained by aconstraining means 250 c described herein (e.g., a cuff) to preventdivarication of the fronds from the delivery catheter. When the targetlocation is reached at Os O or other selected location, the constrainingmeans 250 c is released by the expansion of balloon 32 or otherconstraint release means described herein (alternatively, theconstraining means can be released prior to balloon expansion). Balloon32 is then further expanded to expand and implant the support region 12within the branch vessel lumen BVL, as shown in FIGS. 10A and 10B.Expansion of the balloon 32 also partially deploys the fronds 16, asshown in FIGS. 10A and 10B, typically extending both circumferentiallyand axially into the main vessel lumen MVL. The fronds 16, however, arenot necessarily fully deployed and may remain at least partially withinthe central region of the main vessel lumen MVL. In another embodiment,the constraining means can be released after balloon expansion.

In another embodiment for stent deployment, after deploying stent 10,the cuff or other constraining means 250 c need not be removed but canremain in position over at least a portion of the fronds so as toconstrain at least the tip of the fronds. See, e.g., FIG. 12A, discussedin additional detail below. Then a main vessel stent 150 is advancedinto the main vessel to at least partially overlap the fronds asdescribed above. This method provides a reduced chance that thefrond-tips will caught in or on the advancing main vessel stent 150because the fronds are still captured under the cuff. After placement ofstent 150 balloon 32 together the 12 stent portion of the side branchprosthesis is deployed by inflation of 30 balloon. Prosthesis deliverysystem including cuff 250 c are removed (by pulling on catheter 30) torelease the fronds which when released, spring outward to surround asubstantial portion of the circumference of the main vessel stent 150and the delivery procedures continues as described herein. This approachis also desirable in that by having the cuff left on over the fronds,the frond-tips are constrained together resulting in more advancement ofthe main vessel stent 150. This in turn can reduce procedure time andincrease the accuracy and success rate in placement of the main vesselstent 150 particularly with severely narrowed, eccentric, or otherwiseirregularly shaped lesions. In various embodiments, cuff 250 c and/orproximal end of balloon 32 can have a selectable amount of taperrelative to the body of the balloon to facilitate advancement of one orboth of the main vessel stent 150 or stent 10 into the target tissuesite when one device has already been positioned. Such embodiments alsofacilitate placement into severely narrowed vessels and/or vessels withirregularly shaped lesions.

Various approaches can be used in order to fully open the fronds 16. Inone embodiment, a second balloon catheter 130 can be introduced over aguidewire GW to position the second balloon 132 within the fronds, asshown in FIGS. 11A and 11B. Optionally, the first catheter 30 could bere-deployed, for example, by partially withdrawing the catheter,repositioning the guidewire GW, and then advancing the deflated firstballoon 32 transversely through the fronds 16 and then re-inflatingballoon 32 to fully open fronds 16. A balloon which has been inflatedand deflated generally does not refold as nicely as an uninflatedballoon and may be difficult to pass through the fronds. It willgenerally be preferable to use a second balloon catheter 130 for fullydeforming fronds 16. When using the second balloon catheter 130, asecond GW will usually be prepositioned in the main vessel lumen MVLpast the Os O, as shown in FIGS. 11A and 11B. Further details of variousprotocols for deploying a prosthesis having a stent region (12) andfronds or anchors, such as prosthesis 10, are described in co-pendingapplication Ser. No. 10/807,643.

In various embodiments for methods of the invention usingprosthesis/delivery system 5, the physician can also make use ofadditional markers 22 and 24 positioned at the proximal and distal endsof the prosthesis 10. In one embodiment, one or more markers 22 arepositioned at the proximal ends of the fronds as is shown in FIGS. 9Aand 9B. In this and related embodiments, the physician can utilize themarkers to ascertain the axial position of the stent as well as thedegree of deployment of the fronds (e.g., whether they are in captured,un-captured or deployed state). For example, in one embodiment of thedeployment protocol, the physician could ascertain proper axialpositioning of the stent by not only aligning the transition marker 20with the Os opening O, but also look at the relative position of endmarkers 22 in the main vessel lumen MVL to establish that the fronds arepositioned far enough into the main vessel, have not been inadvertentlypositioned into another branch vessel/lumen. In this way, markers 20 and22 provide the physician with a more accurate indication of proper stentpositioning in a target location in a bifurcated vessel or lumen.

In another embodiment of a deployment protocol utilizing markers 22, thephysician could determine the constraint state of the fronds (e.g.capture or un-captured), by looking at the position of the markersrelative to balloon 30 and/or the distance between opposing fronds. Inthis way, markers 22 can be used to allow the physician to evaluatewhether the fronds were properly released from the constraining meansprior to their deployment. In a related embodiment the physician coulddetermine the degree of deployment of the fronds by looking at (e.g.,visual estimation or using Quantitative Coronary Angiography (QCA)) thetransverse distance between markers 22 on opposing fronds using one ormedical imaging methods known in the art (e.g., fluoroscopy). If one ormore fronds are not deployed to their proper extent, the physician coulddeploy them further by repositioning (if necessary) and re-expandingballoon catheters 30 or 130.

Referring now to FIG. 12A-12I, an exemplary and embodiment of adeployment protocol using a deployment system 5 having a prosthesis 10with fronds 16 will now be presented. As shown in FIG. 12A, prosthesis10 is positioned at Os opening O with catheter 30 such that the stentsection 12 is positioned substantially in branch vessel BV with thefronds 16 extending into the Os O and in the main vessel lumen MVL. Inthis embodiment a second delivery catheter 130 containing a stent 150has been positioned in the MVL prior to positioning of catheter 30.Alternatively, catheter 130 can be positioned first and the branchvessel catheter 30 subsequently. In embodiments where catheter 130 hasbeen positioned first, the proximal end of catheter 30 including fronds16 can be positioned adjacent a proximal portion of balloon 132 ofcatheter 130 such that portions of captured fronds 16 and stent 150 arepositioned side by side. Such alignment can be facilitated by lining upone or more radio-opaque markers (described herein) on the twocatheters.

Next, as shown in FIGS. 12B-12C, balloon 32 of catheter 30 is expanded.Then as shown in FIGS. 12D-12E, catheter 30 together with cuff 250 c iswithdrawn from the vessel to uncover and release the fronds 16. Whendeployed, the fronds 16 are positioned between the vessel wall and stent150 and substantially surround at least a portion of the circumferenceof the main vessel stent 150C/delivery system (130) as well as makingcontact with a substantial portion of inner wall Wm of main vessel lumenMVL. Preferably as shown in FIG. 12E, the fronds are distributed aroundthe circumference of the Wall Wm. Also as shown in FIG. 12E one of thefronds 16A may bent back by stent 150, but may not be contacting thevessel wall.

Then, as shown in FIGS. 12F-12H, balloon 132 is expanded to expand anddeploy stent 150 after which the balloon is deflated and catheter 130 iswithdrawn. Expansion of stent 150 serves to force and hold fronds 16 upagainst the vessel wall in a circumferential pattern as is shown in FIG.12G. This essentially fixes the fronds in place between expanded stent150 and the vessel wall. As such, the fronds may serve five functions,first, as an anchoring means to hold stent 12 in place in the branchvessel lumen BVL. Second they serve as a mechanical joining means tomechanically join stent 12 to stent 150. Third, to provide stentcoverage to prevent prolapse of tissue into the lumen as well as in thecase of a drug coated stent to deliver agent. Finally, they also provideadditional mechanical prosthesising (hoop strength) to hold open Os ofthe branch vessel. More specifically, the now fixed fronds 16 can beconfigured to serve as longitudinal struts to more evenly distributeexpansion forces over a length of the vessel wall as well as distributecompressive forces over a length of stent 12.

The prosthesis of the present invention, may be utilized in combinationwith either main vessel stents having a substantially uniform wallpattern throughout, or with main vessel stents which are provided with awall pattern adapted to facilitate side branch entry by a guidewire, toenable opening the flow path between the main vessel and the branchvessel. Three examples of suitable customized stent designs areillustrated in FIG. 13A through 13C. In each of these constructions, amain vessel stent 110 contains a side wall 112 which includes one ormore windows or ports 114. Upon radial expansion of the stent 110, theport 114 facilitates crossing of a guide wire into the branch lumenthrough the side wall 112 of the main vessel stent 110. A plurality ofports 114 may be provided along a circumferential band of the mainvessel stent 110, in which instance the rotational orientation of themain vessel stent 110 is unimportant. Alternatively, as illustrated, asingle window or port 114 may be provided on the side wall 112. In thisinstance, the deployment catheter and radiopaque markers should beconfigured to permit visualization of the rotational orientation of themain vessel stent 110, such that the port 114 may be aligned with thebranch vessel.

In general, the port 114 comprises a window or potential window throughthe side wall which, when the main vessel stent 110 is expanded, willprovide a larger window than the average window size throughout the restof the stent 110. This is accomplished, for example, in FIG. 13A, byproviding a first strut 116 and a second strut 118 which have a longeraxial distance between interconnection than other struts in the stent110. In addition, struts 116 and 118 are contoured to provide a firstand second concavity facing each other, to provide the port 114.

Referring to FIG. 13B, the first strut 116 and second strut 118 extendsubstantially in parallel with the longitudinal axis of the stent 110.The length of the struts 116 and 118 is at least 2 times, and, asillustrated, is approximately 3 times the length of other struts in thestent. Referring to FIG. 13C, the first and second struts 116 and 118are provided with facing concavities as in FIG. 13A, but which arecompressed in an axial direction. Each of the foregoing configurations,upon expansion of the main vessel stent 110, provide an opening throughwhich crossing of a guidewire may be enhanced. The prosthesis of thepresent invention may be provided in kits, which include a prosthesismounted on a balloon catheter as well as a corresponding main vesselstent mounted on a balloon catheter, wherein the particular prosthesisand main vessel stent are configured to provide a working bifurcationlesion treatment system for a particular patient. Alternatively,prostheses in accordance with the present invention may be combined withseparately packaged main vessel stents from the same or other supplier,as will be apparent to those of skill in the art.

FIG. 13D is an image of a main vessel stent having a side opening,deployed such that the side opening is aligned with the branch vessellumen.

In accordance with a further aspect of the present invention, there isprovided a stepped balloon for use with the prosthesis disclosed herein.The stepped balloon may be utilized for the initial implantation of theprosthesis, or for reconfiguring a previously implanted prosthesis aswill be apparent to those of skill in the art.

Referring to FIG. 15, there is illustrated a schematic side view of adistal end section of a catheter 150 having an elongate flexible tubularshaft 152 with a stepped balloon 154 mounted thereon. The dimensions,materials and construction techniques for the catheter shaft 152 arewell understood in the art, and discussed briefly elsewhere herein. Ingeneral, shaft 152 has an axial length sufficient to reach from thedesired percutaneous access point to the treatment site, and willtypically include at least one inflation lumen for placing the steppedballoon 154 in fluid communication with a source of inflation media, aswell as a guidewire lumen for either over the wire or rapid exchangeguidewire tracking.

The stepped balloon 154 extends between a proximal end 156 and distalend 158. The balloon 154 is necked down to the catheter shaft 152 ateach of the proximal and distal ends, and secured to the shaft 152 usingany of a variety of adhesives, thermal bonding, or other techniques wellknown in the art.

The stepped balloon is provided with a proximal zone 160 and a distalzone 162, separated by a transition zone 164. In the illustratedembodiment, the proximal zone 160 has a greater inflated diameter thanthe distal zone 162. Alternatively, the relative dimensions may bereversed, such that the distal zone 162 has a greater inflated diameterthan the proximal zone 160, such as for use in a retrogradecatheterization from the branch vessel into the main vessel.

The diameters and lengths of the proximal zone 160 and distal zone 162may be varied considerably, depending upon the intended target site. Inan implementation of the invention designed for use in the coronaryartery, a proximal zone 160 may be provided with a diameter in the rangeof from about 3 mm to about 4 mm, and the distal zone 162 may have aninflated diameter in the range of from about 2 mm to about 3 mm. In oneimplementation of the invention, the proximal zone 160 has an inflateddiameter of about 3.5 mm and the distal zone 162 has an inflateddiameter of about 2.5 mm. In general, the inflated diameter of theproximal zone 160 will be at least 110% of the inflated diameter of thedistal zone 162. In certain implementations of the invention, theinflated diameter of the proximal zone 160 will be at least 125% of theinflated diameter of the distal zone 162.

The proximal zone 160 has a working length defined as the axial lengthbetween a proximal shoulder 166 and a distal shoulder 168. The workinglength of the proximal zone 160 is generally within the range of fromabout 5 to about 30 mm, and, in one embodiment, is about 9 mm. Theworking length of the distal zone 162 extends from a proximal shoulder170 to a distal shoulder 172. The working length of the distal zone 162is generally within the range of from about 5 to about 20 mm, and, inone embodiment, is about 6 mm. In the illustrated embodiment, each ofthe proximal zone 160 and distal zone 162 has a substantiallycylindrical inflated profile. However, noncylindrical configurations mayalso be utilized, depending upon the desired clinical result.

The configuration and axial length of the transition zone 164 may bevaried considerably, depending upon the desired frond configuration andostium coverage characteristics of the implanted prosthesis. In theillustrated embodiment, the transition zone 164 comprises a generallyfrustoconical configuration, having an axial length between proximalshoulder 170 of the distal zone 162 and distal shoulder 168 of theproximal zone 160 within the range of from about 1 to about 10 mm, and,in one embodiment, about 2.5 mm.

The transition zone of this balloon delineates the transition from onediameter to another. In one embodiment this transition zone may be 4 mmin length and ramp from 2.5 to 3.5 mm in diameter. This conical surfaceis used to mold or flare the ostium of the bifurcation from the smallerside branch to the larger main vessel. In this configuration thisstepped balloon may be utilized for deploying the prosthesis. Used inthis manner the leading and trailing surfaces are utilized to expand thedevice in the side branch and main vessel and the transition zone isused to flare the transition zone of the stent against the wall of theostium.

The wall of the stepped balloon 154 may comprise any of a variety ofconventional materials known in the angioplasty balloon arts, such asany of a variety of nylons, polyethylene terephthalate, variousdensities of polyethylene, and others known in the art. Materialselection will be influenced by the desired compliancy and burststrength of the balloon, as well as certain manufacturingconsiderations.

The stepped balloon may be formed in accordance with techniques wellknown in the angioplasty arts. For example, stock tubing of the desiredballoon material may be inflated under the application of heat within aTeflon lined capture tube having the desired stepped configuration. Theproximal and distal ends may thereafter be axially stretched with theapplication of heat to neck down to a diameter which relatively closelyfits the outside diameter of the elongate shaft 152.

The balloon may be constructed such that it assumes the inflated steppedconfiguration at a relatively low inflation pressure. See, e.g., anexemplary compliance curve in FIG. 16. Alternatively, the balloon may beconfigured for sequential expansion, such as by allowing the distal zone162 to inflate to its final outside diameter at a first pressure, tofirmly position the branch vessel stent, and the proximal zone 160 onlyinflates to its final diameter at a second, higher inflation pressure,where a sequential deployment of the implant is desired.

In one embodiment the balloon is constructed such that it assumes theinflated stepped configuration upon inflation and retains this shapethroughout its inflated working range (from initial inflation to ratedburst pressure.) In this embodiment the balloon working range is from 1ATM to 16 ATM at rated burst pressure.

In another embodiment the balloon is constructed such that it initiallyassumes the inflated stepped configuration within the lower pressures ofits working range and trends to the same diameter at the higherpressures. The diameter of this balloon at higher pressure approximatesthat of the larger diameter in the stepped configuration.

In another embodiment the balloon is constructed such that it initiallyhas a single diameter during the initial lower pressures of its workingrange and assumes its inflated stepped configuration at higherpressures. The diameter of the balloon at lower pressure approximatesthat of the smaller diameter in the stepped configuration.

Alternatively, the function of the stepped balloon 154 may beaccomplished by providing two distinct balloons, 160′ and 162′. Theproximal balloon 160′ may be inflated by a first inflation lumen (notillustrated) and the distal balloon 162′ may be inflated by a secondinflation lumen (not illustrated) extending throughout the length of thecatheter shaft, to separate inflation ports. Inflation may beaccomplished simultaneously or sequentially, depending upon the desiredclinical procedure. Alternatively, a proximal balloon 160′ and a distalballoon 162′ may be both inflated by a single, common inflation lumenextending throughout the length of the catheter shaft.

The stepped balloon 154 is preferably navigated and positioned withinthe vascular system under conventional fluoroscopic visualization. Forthis purpose, the catheter 150 may be provided with at least oneradiopaque marker. In the illustrated embodiment, a first radiopaquemarker 174 is provided on the catheter shaft 152, at about the proximalshoulder 166. At least a second radiopaque marker 176 is provided on theshaft 152, aligned approximately with the distal shoulder 172. Proximalmarker 174 and distal marker 176 allow visualization of the overalllength and position of the stepped balloon 154.

In addition, a first transition marker 178 and second transition marker180 may be provided on the shaft 152, at a location corresponding to atransition zone on the prosthesis. Transition markers 178 and 180 thusenable the precise location of the prosthesis transition with respect tothe ostium between the main vessel and branch vessel, as has beendiscussed elsewhere herein. Each of the markers may comprise a band ofgold, silver or other radiopaque marker materials known in the catheterarts.

In one embodiment of the stepped balloon 154 intended for use in thecoronary artery, the axial length of the balloon between the proximalmarker 174 and distal marker 176 is approximately 19.5 mm. The lengthbetween the distal marker 176 and transition marker 180 is approximately6.1 mm. The distance between the transition markers 178 and 180,including the length of the transition markers, is about 4.5 mm. As willbe apparent to those of skill in the art other dimensions may beutilized, depending upon the dimensions of the prosthesis and the targetanatomy.

Referring to FIGS. 17 and 18, there is schematically illustrated twodifferent configurations of a stepped balloon 154 in accordance with thepresent invention, positioned and inflated within a treatment site at avascular bifurcation, with the prosthesis omitted for clarity. In each,a stepped balloon 154 is positioned such that a proximal zone 160 isinflated within a main vessel 182. A distal zone 162, having a smallerinflated diameter than proximal zone 160, is positioned within thebranch vessel 184. The stepped balloon 154 has been positioned toillustrate the relative location of the transition markers 178 and 180,with respect to the carina 186 of the bifurcation.

FIGS. 19 through 22 illustrate one application of the stepped balloonand prosthesis in accordance with the present invention. Referring toFIG. 19, there is illustrated a bifurcation between a main vessel 200and a branch vessel 202. A main vessel guidewire 204 is illustrated aspositioned within the main vessel, and a branch vessel guidewire 206 isin position extending from the main vessel 200 into the branch vessel202.

A balloon catheter 208 carrying a prosthesis 210 is advancing along thebranch vessel guidewire 206.

Referring to FIG. 20, the catheter 208 has advanced to the point ofpositioning the prosthesis 210 across the ostium between the main vessel200 and branch vessel 202.

Referring to FIG. 21, a stepped balloon 212 carried by the catheter 208has been inflated across the ostium into the branch vessel 202. FIG. 22illustrates the implanted prosthesis 210, after the balloon catheter 208has been proximally retracted.

As can be seen from FIGS. 21 and 22, dilation of the stepped balloon 212across the ostium enables expansion of the distal zone of the prosthesisin the branch vessel, the proximal zone of the prosthesis in the mainvessel, and a transition zone of the prosthesis spans the ostium. Themain vessel guidewire 204 may thereafter be proximally retracted to apoint proximal to the prosthesis 212, and distally advanced through theproximal portion and the fronds of the prosthesis. A main vessel stentmay thereafter be positioned in the main vessel 200 as has beendiscussed elsewhere herein.

Referring to FIGS. 23 and 24, there is illustrated a schematicrepresentation of a distal portion of a stepped balloon catheter inaccordance with the present invention. In general, the catheter includesa primary guidewire lumen as is understood in the art, such as fortracking the guidewire which extends into the branch vessel. Unlikeprevious embodiments disclosed herein, the catheter of FIGS. 23 and 24includes a secondary guidewire lumen, such as for tracking the guidewirewhich extends into the main vessel lumen beyond the bifurcation.

Referring to FIG. 23, a catheter 220 extends between a proximal end 222(not shown) and a distal end 224. A balloon 226 is carried in vicinityof the distal end 224, as is known in the balloon catheter arts. Balloon226 may comprise a stepped balloon as has been described elsewhereherein, or a tapered balloon, or a conventional cylindrical angioplastyor stent deployment balloon, depending upon the desired performance.

The catheter 220 includes a guidewire lumen 228 which extends throughoutthe length of at least a distal portion of the catheter 220, to a distalport 230 at the distal end 224 of the catheter 220. In an embodimentintended for over-the-wire functionality, the first guidewire lumen 228extends proximally throughout the length of the catheter, to a proximalmanifold. In an alternate configuration intended for rapid exchangefunctionality, a proximal access port (not shown) provides access to thefirst guidewire lumen 228 at a point along the length of the catheterdistal to the proximal end 222. In general, rapid exchange proximalaccess ports may be within the range of from about 10 cm to about 30 cmfrom the distal end 224.

As can be seen with reference to, for example, FIG. 23A, the catheter220 is additionally provided with an inflation lumen 232 which extendsthroughout the length of the catheter to the proximal end 222. Thedistal end of inflation lumen 232 is in communication via an inflationport 234 with the interior of the balloon 226, to enable placement ofthe balloon 226 in fluid communication with a source of inflation media.

Referring to FIG. 23B, the catheter 220 is additionally provided with asecond guidewire lumen 236. Second guidewire lumen 236 extends between aproximal access port 238 and a distal access port 240. The distal accessport 240 is positioned proximally to the distal end 224 of the catheter220. In the illustrated embodiment, the distal port 240 is positioned onthe proximal side of the balloon 226. Generally, the distal port 240will be no greater than about 4 cm, and often no greater than about 2 cmproximal of the balloon 226.

The proximal access port 238 may be provided on the side wall of thecatheter, such as within the range of from about 10 cm to about 60 cmfrom the distal end 224. In one embodiment, the proximal access port 238is within the range of from about 25 cm to about 35 cm from the distalend 224. The proximal port 238 is preferably spaced distally apart fromthe proximal end 222 of the catheter 220, to enable catheter exchangewhile leaving the main vessel guidewire in place as will be apparent inview of the disclosure herein.

As illustrated in FIG. 23, the second guidewire lumen 236 may be formedas an integral part of the catheter body. This may be accomplished byproviding an initial 3 lumen extrusion having the desired length, andtrimming away the wall of the second guidewire lumen 236 distally of thedistal port 240 and proximally of the proximal port 238.

Alternatively, the second guidewire lumen 236 may be separately attachedto a conventional catheter shaft such as is illustrated in FIG. 24. Inthis construction, the second guidewire lumen 236 is defined within atubular wall 237, which may be a separate single lumen extrusion. Thetubular wall 237 is positioned adjacent the catheter shaft, and bondedthereto using any of a variety of techniques known in the art, such asthermal bonding, adhesives, solvent bonding or others. Superior bondingand a smooth exterior profile may also be achieved by placing a shrinktube around the assembly of the catheter 220 and tubular wall 237, andheating the shrink tube to shrink around and combine the two structuresas is well understood in the catheter manufacturing arts. It may bedesirable to place a mandrel within the second guidewire lumen 236 andpossibly also the first guidewire lumen 228 and inflation lumen 232during the heat shrinking process.

In use, the second guidewire lumen 236 enables control over the mainvessel guidewire. Referring to FIG. 25, there is illustrated a twoguidewire catheter 208 in position across a bifurcation from a mainvessel 200 into a branch vessel 202. The branch vessel guidewire 206 hasbeen positioned in the branch vessel 202, and the catheter 208 advancedinto position over the wire into the bifurcation. The prosthesis 210 isillustrated in its expanded configuration, and the balloon has beendeflated.

Prior to percutaneously introducing the catheter into the patient'svasculature, the main vessel guidewire 204 is positioned within thesecondary guidewire lumen 236, and the catheter and main vesselguidewire assembly is advanced as a unit along the branch vesselguidewire to the treatment site.

As seen in FIG. 25, the distal exit port 240 of the secondary guidewirelumen 236 is aligned such that the main vessel guidewire 204 is aimeddown the lumen of the main vessel 200. In the illustrated embodiment,the secondary guidewire lumen is attached to the outside of the stepballoon. The stent is crimped onto the step balloon, and the exit of thesecondary guidewire lumen is between the intermediate zone and thecircumferentially extending link of the prosthesis. In the crimpedconfiguration, the distal exit 240 of the secondary lumen 236 residesbetween two adjacent fronds.

Following deployment of the stent and deflation of the balloon asillustrated in FIG. 25, the main vessel guidewire 204 may be distallyadvanced into the main vessel beyond the bifurcation, in between the twoadjacent fronds. See, FIG. 26.

Referring to FIG. 27, there is illustrated an embodiment similar to FIG.25, except that the distal exit port 240 of the main vessel guidewirelumen 236 is positioned proximally of the balloon. The precise locationof the distal exit 240 may be varied, so long as it permits direction ofthe main vessel guidewire distally within the main vessel beyond thebifurcation. In general, the distal exit 240 may be located within theaxial length of the prosthesis as mounted on the catheter.

Following distal advance of the main vessel guidewire 204 into the mainvessel distally of the bifurcation, the catheter 208 may be proximallywithdrawn from the treatment site leaving the main vessel guidewire 204in place. The catheter 208 may be removed from the main vessel guidewire204 as is understood in the rapid exchange catheter practices, and asecondary catheter may be advanced down the main vessel guidewire suchas to dilate an opening between the fronds into the main vessel beyondthe bifurcation and/or deploy a second stent at the bifurcation as hasbeen discussed herein.

In FIGS. 25 through 27, the catheter 208 is schematically illustrated asa construct of a separate main vessel lumen attached to a catheter body.However, in any of the foregoing catheters the body construction may bethat of a unitary extrusion as has been discussed previously.

The stepped balloon of the present invention may be used in a variety ofadditional applications. For example, the distal lower diameter sectionof the device may be used to slightly open a small blood vessel then thesystem advanced to treat the index lesion with an appropriately sizedcatheter. In one embodiment the stepped balloon may function as astandard PTCA catheter for the treatment of advanced cardiovasculardisease. Specifically in cases where only a small diameter ballooncatheter is capable of crossing a diseased lesion, the smaller diameterleading portion of the step balloon may be used to predilate the lesion.The catheter would then be deflated and the larger diameter trailingsegment advanced across the lesion. The larger diameter portion of thestepped balloon would then be used to dilate the diseased lesion to alarger diameter. In this way the stepped balloon functions as both apre-dilation and final dilation catheter.

FIGS. 28-29 illustrate some of the advantages of the link system 714discussed above in connection with FIGS. 2N-2O. FIG. 28 shows therelationship of a prosthesis 700′ that is similar to the prosthesis 700except that the prosthesis 700′ includes a circumferential link 714′with a single filament member extending circumferentially between eachof a plurality of fronds. The prosthesis 700′ is shown mounted on adelivery catheter that includes a balloon. The arrow A points to aportion of a frond that is lifting off of the balloon. This can becaused by a number of factors in use, such as a decrease in the distancebetween the link 714′ and a stent section 704′, with a lesser shorteningof the frond. As can be seen, the frond is lifting away from the surfaceof the balloon in the middle of the frond. This lifting createssufficient torque at the proximal end of the prosthesis 700′ to deformthe circumferential link 714′ to some degree. Such deformation can causethe link 714′ to be displaced into the central area of the prosthesis,which can cause problems for subsequent treatment steps, such as duringintroduction of a main vessel stent through the single filament link714′.

FIG. 29 illustrates the prosthesis 700 with the link system 714 mountedon a balloon B. As discussed above, the frond engagement portion 744 isadapted to absorb a substantial amount of torque from the frond section712 without transmitting it to the catheter securement portion 752.These structures lessen the deformation of the catheter securementportion 752 and the tendency of the catheter securement portion 752 tobe displaced into the central area of the prosthesis 700. The frondengagement portion 744 helps to maintain the crimped profile of thefronds as the device navigates through tortuous vasculature such as thecoronary arteries. The link system 714, particularly the frondengagement portion 744, helps to maintain the uniform spacing of thefronds during deployment. The catheter securement portion 752facilitates re-entry into a guiding catheter, if required, by enhancingthe force required to dislodge the prosthesis 700 during retractionbased on surface area and frictional engagement between the link system714 and the balloon. In addition, the effects of the motion of thefronds in the frond section 712 is primarily absorbed by the frondengagement portion 744 thus allowing the catheter securement portion 752to maintain its crimped profile. Thus, subsequent steps of a procedureare facilitated, such as the passing of a main vessel stent through theproximal end of the prosthesis and through a side-wall opening definedbetween adjacent fronds, as described above.

Although the present invention has been described primarily in thecontext of a prosthesis adapted for positioning across the Os between abranch vessel and a main vessel prior to the introduction of the mainvessel stent, in certain applications it may be desirable to introducethe main vessel stent first. Alternatively, where the prosthesis of thepresent invention is used provisionally, the main vessel stent may havealready been positioned at the treatment site. The main vessel stent mayinclude a side branch opening, or a side branch opening may be formed byadvancing a balloon catheter through the wall of the stent in thevicinity of the branch vessel. Thereafter, the prosthesis of the presentinvention may be advanced into the main vessel stent, though the sidewall opening, and into the branch vessel, with the circumferential linkpositioned within the interior of the main vessel stent. In many of theembodiments disclosed herein, the circumferential link will expand to adiameter which is approximately equal to the expanded diameter of thebranch vessel support. Thus, upon initial deployment of the prosthesis,the circumferential link may be expanded to a diameter which is lessthan the adjacent diameter of the main vessel. If the prosthesis of thepresent invention is positioned within a previously positioned mainvessel stent, it may therefore be desirable to include a post dilatationstep to expand the circumferential link up to the inside diameter of themain vessel stent and also to deform the fronds outwardly androtationally to conform to the interior surface of the main vesselstent.

While the above is a complete description of the preferred embodimentsof the invention, various alternatives, modifications, and equivalentsmay be used. Also, elements or steps from one embodiment can be readilyrecombined with one or more elements or steps from other embodiments.Therefore, the above description should not be taken as limiting thescope of the invention which is defined by the appended claims.

What is claimed is:
 1. A prosthesis for placement at an ostium openingfrom a main body lumen to a branch body lumen, the prosthesiscomprising: a radially expansible support configured to be deployed inat least a portion of the branch body lumen; a plurality of longitudinalmembers extending from either a proximal or distal end of the support,the longitudinal members configured to be positioned in the main bodylumen; and a circumferential member, wherein at least one of thelongitudinal members further comprises a first end and a second end, thefirst end coupled with a portion of the prosthesis distal of the secondend, and the second end coupled with the circumferential member, whereinat least one other longitudinal member is not coupled with thecircumferential member.
 2. The prosthesis of claim 1, wherein the atleast one other longitudinal member comprises a frond not coupled withthe circumferential member.
 3. The prosthesis of claim 1, wherein thesupport has a first wall pattern, and the prosthesis comprises atransition portion disposed between the support and the circumferentialmember that has a second wall pattern different from the first wallpattern.
 4. The prosthesis of claim 3, wherein the transition portionhas a circumferential surface area that is higher toward the first endof the transition portion and lower toward the second ends of thetransition portion.
 5. The prosthesis of claim 3, wherein proximal endsof the transition portion are configured to reach a location in theproximal main body lumen and a location in the distal main body lumen.6. The prosthesis of claim 3, wherein the proximal ends of thetransition portion are configured to open up in different direction tofollow the ostium opening.
 7. The prosthesis of claim 3, wherein thetransition portion is coupled with apices on the support, the transitionportion having a first plurality of side-by-side filaments and a secondlesser plurality of side-by-side filaments.
 8. The prosthesis of claim1, wherein the circumferential member is configured to anchor thesupport.
 9. The prosthesis of claim 1, wherein the longitudinal membercomprises is a single filament.
 10. The prosthesis of claim 1, whereinthe longitudinal member comprises a serpentine or sinusoidal member. 11.The prosthesis of claim 1, wherein the longitudinal member comprises adual serpentine member.
 12. The prosthesis of claim 1, wherein thelongitudinal member is configured to act as a compression membertransferring force applied to the support or applied to the transitionportion to the circumferential member.
 13. The prosthesis of claim 1,wherein the longitudinal member is configured to act as a tension membercapable of resisting tensile force of a magnitude applied duringdeployment.
 14. The prosthesis of claim 1, wherein the longitudinalmember is configured to be a compression and a tension member.
 15. Theprosthesis of claim 1, wherein the circumferential member comprises twocircumferential rings coupled together with an axial link.
 16. Theprosthesis of claim 1, wherein at least one of the longitudinal memberscomprises a frond.
 17. The prosthesis of claim 16, wherein the at leastone frond comprises a transition portion having a first end coupled withthe support and a plurality of second ends spaced apart from thesupport.
 18. A prosthesis for placement at an opening from a main bodylumen to a branch body lumen, the prosthesis comprising: a radiallyexpansible support configured to be deployed in at least a portion ofthe branch body lumen, the support adapted to provide a radial force tosupport the branch body lumen; a plurality of longitudinal membersextending from an end of the support, the longitudinal membersconfigured to reach into the main body lumen when deployed; and acircumferential member spaced apart from the support and providing asecond radial strength less than the first radial strength whendeployed, the circumferential member connected to at least one of thefronds and unconnected to at least one other frond.
 19. The prosthesisof claim 18, wherein the longitudinal members comprise a transitionportion, and the at least one of the longitudinal members connected tothe circumferential member further comprises an elongate portion havinga first end coupled with the transition portion and a second end coupledwith the circumferential member.
 20. The prosthesis of claim 18, whereinthe longitudinal members are configured to reach a location in theproximal main body lumen and a location in the distal main body lumen.21. A prosthesis for placement at an ostium opening from a first bodylumen to a second body lumen, the prosthesis comprising: a radiallyexpansible support configured to be deployed in at least a portion ofthe first body lumen; at least two longitudinal members extending froman end of the support, all of the longitudinal members configured to bepositioned in the second body lumen when deployed; and a circumferentialmember connected to at least one of the fronds and unconnected to atleast one other frond.
 22. The prosthesis of claim 21, wherein the atleast one longitudinal members connected to the circumferential memberis configured to be disposed in the second body lumen in an upstream ordownstream direction from the ostium when deployed.
 23. The prosthesisof claim 21, wherein the circumferential member is configured to bepositioned in the second body lumen when deployed.